Posoleucel in Kidney Transplant Recipients with BK Viremia

Visual Abstract

Abstract

Key Points

• Posoleucel was generally safe, well tolerated, and associated with a greater reduction of BK viremia compared with placebo.

• BK viremia reduction occurred coincident with an increase in the circulating frequency of BK virus–specific T cells in posoleucel recipients.

• The presence and persistence of posoleucel was confirmed by T-cell receptor variable β sequencing.

Background

Kidney transplant recipients with BK virus infection are at risk of developing BK virus–associated nephropathy, allograft rejection, and subsequent graft loss. There are no approved treatments for BK virus infection. Posoleucel is an off-the-shelf, allogeneic, multivirus-specific T-cell investigational therapy targeting BK virus, as well as five other opportunistic viruses: adenovirus, cytomegalovirus, Epstein–Barr virus, human herpesvirus 6, and John Cunningham virus.

Methods

In this phase 2, double-blind study, kidney transplant recipients with BK viremia were randomized 1:1:1 to receive posoleucel weekly for 3 weeks and then every 14 days (bi-weekly dosing) or every 28 days (monthly dosing) or placebo for 12 weeks. Participants were followed for 12 weeks after completing treatment. The primary objective was safety; the secondary objective was plasma BK viral load reduction.

Results

Sixty-one participants were randomized and dosed. Baseline characteristics were similar across groups. No deaths, graft-versus-host disease, or cytokine release syndrome occurred. The proportion of patients who had adverse events (AEs) judged by the investigators to be treatment-related was slightly lower in recipients of posoleucel: 20% (4 of 20 patients) and 18% (4 of 22) in those infused on a bi-weekly and monthly schedule, respectively, and 26% (5 of 19) in placebo recipients. None of the grade 3–4 AEs or serious AEs in any group were deemed treatment-related. No deaths, graft-versus-host disease, or cytokine release syndrome occurred. Three participants had allograft rejection, but none were deemed treatment-related by investigators. In posoleucel recipients, BK viremia reduction was associated with an increase in the circulating frequency of BK virus–specific T cells, and the presence and persistence of posoleucel was confirmed by T-cell receptor sequencing.

Conclusions

Posoleucel was generally safe, well tolerated, and associated with a larger reduction of BK viremia compared with placebo. Limitations of this study include the relatively short duration of follow-up and lack of power to detect significant differences in clinical outcomes.

Clinical Trial registry name and registration number:

Study of Posoleucel (Formerly Known as ALVR105; Viralym-M) in Kidney Transplant Patients With BK Viremia, NCT04605484.

Introduction

The seroprevalence of BK virus in the adult population is estimated to be as high as 90%.^1,2 In immunocompetent hosts, the virus is held in check by BK virus–specific T cells but can reactivate when the immune system is suppressed. Because of the high level of immunosuppression required to prevent allograft rejection and the ischemic injury associated with kidney transplantation, kidney transplant recipients are highly susceptible to BK virus reactivation. In the first 2 years after transplant, up to 30% of kidney transplant recipients become viremic.^3,4 Clinically, high-level (>10,000 copies/ml) BK viremia is considered presumptive BK virus–associated nephropathy.^5,6 This disease, which occurs in up to 10% of kidney transplant recipients and is characterized by tubulointerstitial nephropathy, often leads to kidney dysfunction and can precipitate graft loss.^6–11 There are no approved BK virus–targeted antiviral therapies. In kidney transplant recipients, the standard of care remains reduction of immunosuppression.¹² Such reduction is not universally effective and is associated with a substantially higher risk of allograft rejection and de novo donor-specific antibody (DSA) formation due to the untargeted nature of immunosuppressive intervention, which generally augments immunity rather than selectively augmenting the BK virus–reactive T-cell subset.^13,14

Posoleucel is an off-the-shelf, allogeneic, multivirus-specific T-cell therapy designed to address the underlying immune deficit in kidney transplant recipients. Posoleucel is manufactured from peripheral blood mononuclear cells obtained from healthy donors with confirmed seropositivity for BK virus as well as adenovirus, cytomegalovirus, Epstein–Barr virus, and human herpesvirus 6. These cells are cultured with viral peptides spanning immunogenic antigens from each of the target viruses to selectively expand virus-reactive memory T-cell populations. Posoleucel is administered as a partially HLA-matched product to participants, with the best-fit line chosen on the basis of consideration of both the HLA type of the allograft and the participant.

We conducted a randomized, double-blind, placebo-controlled phase 2 study of posoleucel in kidney transplant recipients with BK viremia. This is the first randomized, placebo-controlled trial of a third party T-cell product in this population and the first trial of posoleucel in solid-organ transplant recipients. The primary study objective was safety. Adverse events (AEs) of special interest included graft-versus-host disease (GVHD), cytokine release syndrome (CRS), and infusion reaction. DSAs, defined as anti-HLA antibodies against kidney transplant HLA molecules, were monitored throughout the study. Given that all participants were viremic and at risk of BK virus–associated nephropathy, the key secondary objective was to evaluate the antiviral effects of posoleucel.

Methods

Eligibility Criteria and Study Design

This phase 2, multicenter, randomized, double-blind, placebo-controlled, parallel-group study enrolled participants who had undergone a kidney transplant ≥28 days before enrollment and had a positive whole blood or plasma BK viral load (plasma BK viral load also referred to herein as BK viremia) at a local laboratory obtained ≤90 days before the start of screening. Local laboratory values were verified by the central laboratory, with BK virus plasma viral load levels of 350–10,000,000 copies/ml confirmed at screening for study enrollment. To be enrolled, a suitable posoleucel (PSL) cell line matched with at least two alleles expressed by the allograft and at least one HLA allele of the recipient had to be identified after screening of the relevant HLA reports generated before transplant. All screened individuals had an available, suitable PSL line.

The protocol was approved by the Institutional Review Boards, and all the participants signed an informed consent (ClinicalTrials.gov registry number NCT04605484).

Excluded from enrollment were any individuals who had undergone allogeneic hematopoietic cell transplantation, had evidence or history of GVHD or CRS, uncontrolled or progressive viral (non-BK virus), bacterial or fungal infections, and known or presumed pneumonia. Enrollment was not open to individuals receiving ongoing therapy with high-dose systemic corticosteroids (i.e., prednisone dose >0.5 mg/kg per day or equivalent), those who received or were scheduled to receive abatacept or belatacept within 3 months of screening, or those who received antithymocyte globulin in doses >4.5 mg/kg or alemtuzumab or other immunosuppressive T-cell–targeted monoclonal antibodies <28 days before randomization (see Supplemental Material for full eligibility criteria).

Participants were randomized in a 1:1:1 ratio to three treatment arms. Participants in group 1 received posoleucel every 7 days for 3 weeks and thereafter every 14 days (group 1=bi-weekly) for the remainder of the 12-week dosing period. Participants in group 2 received posoleucel every 7 days for 3 weeks and thereafter every 28 days (group 2=monthly) for the remainder of the 12-week dosing period. Posoleucel was administered as a fixed dose of 4×10⁷ cells in both treatment groups. Participants in the placebo group were administered matching placebo every 7 days for 3 weeks and thereafter every 14 days for the remainder of the 12-week dosing period.

Overall, the total duration of participant participation in the study was 26 weeks (2 weeks for screening, 12 weeks of treatment, and 12 weeks of follow-up). Standard-of-care immunosuppression reduction was permitted per protocol-specified guidelines (Supplemental Figure 1). DSA testing was performed using Luminex single-antigen bead assays with a detection threshold of 1000 mean fluorescent intensity.

End Points

The primary end point was safety as evaluated based on treatment-emergent AEs (TEAEs) and changes in vital signs, physical examinations, and clinical laboratory assessments. The key secondary end point was change in BK viremia in participants receiving posoleucel compared with those receiving placebo.

Exploratory end points included change in BK viremia relative to baseline in posoleucel versus placebo participants, eGFR, and DSA.

Biopsies performed during the study for clinical indication were read by a blinded central reader as prespecified in the study protocol.

To reduce the confounding effects of adjustments in participants' immunosuppression immediately before the study, we conducted a post hoc analysis of outcomes in participants on a stable immunosuppression regimen, defined as a <50% reduction in one of the major immunosuppressive medications (tacrolimus, cyclosporine, sirolimus, everolimus, mycophenolate, azathioprine) within 30 (±2) days before randomization.

Immunoassays

IFN-γ enzyme-linked immunosorbent spot (ELISpot) analysis was used to determine the frequency (spot-forming cells) of BK virus–specific IFNγ-producing T cells in peripheral blood pretreatment and post-treatment.¹⁵ Peptide pools spanning VP1 and large T antigens were used to assess the frequency of T cells directed to the posoleucel target antigens, and a peptide pool spanning small T (smT) was used to assess T-cell responses to a nontargeted viral antigen (i.e., endogenous immunity). To confirm the presence and determine the persistence of posoleucel clones, high-throughput T-cell receptor variable β (TCRvβ) deep sequencing (Adaptive Biotechnologies, Seattle, WA) was performed on the infused lines and serial recipient peripheral blood samples collected before and after infusion.^16,17 Posoleucel-derived clones were defined as T-cell clones identified within posoleucel but not detected in the circulation of participants before infusion with posoleucel.

Statistical Analysis

No formal sample size determination was made for this study, in which the primary end point was safety and tolerability. Approximately 60 participants were planned to be randomized at approximately 38 clinical sites. Participants (approximately n=20 in each arm) were to be randomized to receive posoleucel (administered at a dose interval of every 14 or 28 days after three initial weekly doses) or placebo. Participants were stratified by screening BK viral load (“low”: 350 to <10,000 copies/ml versus “high”: ≥10,000–10,000,000 copies/ml) at randomization to ensure equal randomization among active and placebo arms for participant populations with high or low viral loads. A minimum of six participants were to be enrolled in each stratum, but the remaining participants could be enrolled in either stratum. For participants missing week 14 or week 24 data, but who were still in the study, the last value available before weeks 14 and 24 was carried over, respectively. Dropouts were not imputed and excluded from data analysis.

Results

Participant Enrollment and Disposition

Eighty-two individuals were screened for eligibility, and all had a suitable, partially HLA-matched PSL cell line. Twenty-one individuals did not qualify for enrollment for reasons ranging from BK viral loads outside of enrollment criteria, kidney dysfunction, neutropenia, and withdrawal of consent before randomization. Sixty-one participants were randomized and dosed: 20 in group 1 (bi-weekly), 22 in group 2 (monthly), and 19 in the placebo group (Figure 1).

Figure 1.

Participant disposition. f/u, follow-up; IS, immunosuppression; PSL, posoleucel.

Participants' Characteristics

Participants' demographics and baseline characteristics were generally balanced among the three treatment groups (Table 1). Supplemental Table 1 presents demographics and characteristics of the participants with stable immunosuppression prerandomization. Details on the six participants who had prerandomization reduction of immunosuppression are given in Supplemental Table 2.

Table 1.

Demographic and disease characteristics of kidney transplant recipients with BK viremia at baseline

Characteristic	Group 1, N=20	Group 2, N=22	PBO, N=19
Sex, n (%)
Male	17 (85)	17 (77)	15 (79)
Female	3 (15)	5 (23)	4 (21)
Median age, yr (range)	59 (21–75)	54 (28–72)	59 (47–75)
Median time from kidney transplant to day 1, yr (range)	0.9 (0.3–4.8)	1.4 (0.3–7.0)	1.1 (0.2–13.6)
BK viral load
Median, copies/ml	9989	8307	5299
Range	334–4,306,799	242–5,421,939	327–7,837,086
Mean, copies/ml	511,820	296,042	449,227
Median, log10 copies/ml (range)	3.97 (2.5–6.6)	3.91 (2.4–6.7)	3.72 (2.5–6.9)
Mean, log10 copies/ml (SD)	4.40 (1.276)	3.98 (1.073)	3.93 (1.160)
BK viral load stratification
350 to <10,000 copies/ml	n=12	n=12	n=11
Median viral load, copies/ml	3609.5	1825.5	1232.0
≥10,000–10,000,000 copies/ml	n=8	n=10	n=8
Median viral load, copies/ml	475,226	40,327	74,909
Median eGFR, ml/min per 1.73 m2 (range)	43.5 (19–61)	52.5 (27–61)	39.0 (20–61)
Immunosuppressive agents, n (%)a
Tacrolimus	17 (85)	20 (91)	17 (89)
Glucocorticoids	14 (70)	19 (86)	12 (63)
Mycophenolate mofetil	4 (20)	10 (45)	6 (32)
Cyclosporin	1 (5)	0	2 (11)
Everolimus	2 (10)	1 (5)	0
Azathioprine	2 (10)	0	0
Sirolimus	0	1 (5)	1 (5)
Other therapies, n (%)
IVIG	1 (5)	0	2 (11)
Cidofovir	0	0	1 (5)
Leflunomide	2 (10)	3 (14)	2 (11)
Participant and cell line HLA matching, n (%)
Class I only	1 (5)	4 (18)	n/a
Class II only	11 (55)	4 (18)	n/a
Class I and II	8 (40)	14 (64)	n/a
Transplant and cell line HLA matching, n (%)
Class I only	0	0	n/a
Class II only	6 (30)	6 (27)	n/a
Class I and II	14 (70)	16 (73)	n/a
Participants with significant IS reduction before randomization, n (%)	0	2 (9)	4 (21)

IS, immunosuppression; IVIG, intravenous immune globulin; PBO, placebo.

^aTotals exceed 100% because most participants received >1 immunosuppressive agent.

Primary Outcome

The primary outcome was the incidence of TEAEs. The proportions of participants who experienced TEAEs were similar in the three groups: 85% of participants (17 of 20) in the bi-weekly posoleucel dosing group, 77% (17 of 22) in the monthly posoleucel dosing group, and 84% (16 of 19) in the placebo group (Table 2). Overall, the most common AEs were headache, coronavirus disease 2019, serum creatinine elevation, and diarrhea. The proportion of participants who experienced AEs judged by the investigator to be treatment-related was slightly higher in the placebo group than among participants receiving posoleucel: 20% (four of 20 participants) in group 1 (more frequent PSL dosing), 18% (four of 22) for the less frequent dosing group (group 2), and 26% (five of 19) for placebo. None of the grade 3–4 AEs or serious AEs in any group were deemed treatment-related. Only one participant discontinued posoleucel treatment due to an AE. This event, renal tuberculosis (TB), was not considered related to treatment by the investigator. Infusion reactions were rare and minor, and there were no deaths, CRS, or GVHD observed in any participant.

Table 2.

Primary outcome—adverse events over 24 weeks

Parameter	Group 1, N=20	Group 2, N=22	PBO, N=19
Any AE, n (%)	17 (85)	17 (77)	16 (84)
Any treatment-related AE, n (%)	4 (20)	4 (18)	5 (26)
Participants with most common treatment-related AEs (>5%), n (%)
Headache	0	3 (14)	3 (16)
Any SAE	2 (10)	2 (9)	0
Any treatment-related SAE	0	0	0
Any grade ≥3 AE	2 (10)	3 (14)	1 (5)
Any AE leading to dose reduction	0	0	0
Any AE leading to therapy discontinuation	1 (5)a	0	0
Events of special interest
Infusion reaction	0	1 (5)	1 (5)
GVHD	0	0	0
Cytokine release syndrome	0	0	0
Rejection	3 (15)	0b	0
DSA	2 (10)	1 (5)	1 (5)

AE, adverse events; DSA, donor-specific antibody; GVHD, graft-versus-host disease; PBO, placebo; SAEs, serious adverse events.

^aThis participant experienced pyelonephritis, renal tuberculosis, and acute respiratory failure that were not deemed to be related to treatment.

^bOne participant in group 2 had a biopsy that was read locally as rejection, but the central reader read it as “cannot determine.”

Three participants had transplant rejection per the central reader. These three cases were in participants who received posoleucel, but none were judged by the investigators to be treatment-related, and the Supplemental Material provides extensive details on these three events. One participant had a history of multiple rejections, including an episode during screening and before posoleucel infusion. One had concomitant renal TB and was read locally as (and treated only for) renal TB, and not rejection, with improvement. The third participant had rejection 68 days after the last dose of posoleucel and subsequent to immunosuppression reduction.

The proportion of participants who developed de novo DSA after study drug infusion was low and similar in posoleucel and placebo groups, 7% and 5%, respectively (Table 2). Of the three participants in the posoleucel group who developed de novo DSAs, only one developed a single antibody against an HLA allele unique to the virus-specific T cell. In addition, among the participants in the posoleucel group who did not develop de novo DSAs, only one participant developed an antibody against an HLA allele unique to the virus-specific T cell, and no DSAs.

eGFR remained stable over the 24 weeks of the study, as would be expected given the short follow-up and the generally prolonged time required for changes in eGFR levels¹⁸ (Supplemental Table 3). While minor fluctuations were observed in laboratory values over time, there were no apparent trends overall or differences between treatment arms.

Secondary Outcomes

Secondary outcomes related to changes in BK viremia in participants receiving posoleucel compared with placebo. Table 3 presents antiviral response outcomes at week 24. Among the 58 participants who completed the study, ten of 20 (50%) participants who were dosed with posoleucel on the bi-weekly schedule and 30% (six of 20) of those dosed monthly achieved a viral load reduction of ≥1 log10 copies/ml (median BK viral load reduction −0.9 log10 BK virus DNA copies/ml [range, −2.1 to 0.1] and −0.45 [−3.5 to 0.5], respectively), compared with 28% (five of 18) in the placebo group (median BK viral load reduction −0.3 log10 copies/ml [−2.1 to 0.3]) (Table 3). Among the 52 participants with stable immunosuppression before randomization, a BK viral load reduction of ≥50% was seen in 85% (17 of 20) and 56% (ten of 18) of participants administered with posoleucel on the bi-weekly versus monthly dosing regimen, compared with 43% (six of 14) in the placebo group at week 24 relative to baseline. In the same subgroup of participants, ten of 20 (50%) participants who were dosed with posoleucel on the bi-weekly schedule and 28% (five of 18) of those dosed monthly achieved a viral load reduction of ≥1 log₁₀ copies/ml (median BK viral load reduction −0.9 log₁₀ BK virus DNA copies/ml [range, −2.1 to 0.1] and −0.45 [−1.8 to 0.5], respectively), compared with 14% (two of 14) in the placebo group (median BK viral load reduction −0.15 log₁₀ copies/ml [−2.1 to 0.3]) (Table 3).

Table 3.

Secondary outcome—antiviral response to posoleucel at week 24

Participants	Group 1	Group 2	Placebo
Participants who completed study	N=20	N=20	N=18
Pts w/BK viral load decreased by ≥1 log10 BK virus DNA copies/ml versus baseline, n (%)	10 (50)	6 (30)	5 (28)
Viral load below the lower limit of quantitation	3 (15)	3 (15)	3 (17)
BK viral load reduction from baseline, median log10 BK virus DNA copies/ml (min, max)	−0.9 (−2.1, 0.1)	−0.45 (−3.5, 0.5)	−0.3 (−2.1, 0.3)
BK viral load ≥50% reduction, n (%)	17 (85)	11 (55)	10 (56)
Participants with stable ISa	N=20	N=18	N=14
Pts w/BK viral load decreased by ≥1 log10 BK virus DNA copies/ml versus baseline, n (%)	10 (50)	5 (28)	2 (14)
Viral load below the lower limit of quantitation	3 (15)	2 (11)	2 (14)
BK viral load reduction from baseline, median log10 BK virus DNA copies/ml (min, max)	−0.9 (−2.1, 0.1)	−0.45 (−1.8, 0.5)	−0.15 (−2.1, 0.3)
BK viral load ≥50% reduction, n (%)	17 (85)	10 (56)	6 (43)
Participants with stable ISa and screening BK virus viral load 350 to <10K c/ml	N=12	N=10	N=10
Pts w/BK viral load decreased by ≥1 log10 BK virus DNA copies/ml versus baseline, n (%)	4 (33)	0	1 (10)
Viral load below the lower limit of quantitation	3 (25)	1 (10)	2 (20)
BK viral load reduction from baseline, median log10 BK virus DNA copies/ml (min, max)	−0.7 (−1.6, 0.05)	0.01 (−0.8, 0.5)	0.09 (−1.4, 0.3)
BK viral load ≥50% reduction, n (%)	10 (83)	3 (30)	4 (40)
Participants with stable ISa and screening BK virus viral load ≥10K c/ml	N=8	N=8	N=4
Pts w/BK viral load decreased by ≥1 log10 BK virus DNA copies/ml versus baseline, n (%)	6 (75)	5 (63)	1 (25)
Viral load below the lower limit of quantitation	0	1 (13)	0
BK viral load reduction from baseline, median log10 BK virus DNA copies/ml (min, max)	−1.4 (−2.1, 0.1)	−1.5 (−1.8, −0.2)	−0.4 (−2.1, −0.01)
BK viral load ≥50% reduction, n (%)	7 (88)	7 (88)	2 (50)
Participants with stable IS,a baseline BK virus viral load ≥5K c/ml and <2 yr after kidney transplant	N=11	N=6	N=6
Pts w/BK viral load decreased by ≥1 log10 BK virus DNA copies/ml versus baseline, n (%)	8 (73)	3 (50)	1 (17)
Viral load below the lower limit of quantitation	1 (9)	1 (17)	0
BK viral load reduction from baseline, median log10 BK virus DNA copies/ml (min, max)	−1.3 (−2.1, 0.1)	−1.1 (−1.8, 0.3)	−0.15 (−2.1, 0.2)
BK viral load ≥50% reduction, n (%)	10 (91)b	4 (67)	2 (33)

IS, immunosuppression; Pts, participants.

^a<50% reduction in calcineurin inhibitors, mammalian target of rapamycin, mycophenolate mofetil/mycophenolic acid, or azathioprine within 30 (±2) days of randomization.

^bP < 0.05.

A larger antiviral effect was seen in participants with a high viral load (≥10,000 copies/ml) at screening. Among those with stable immunosuppression before randomization and a screening viral load of ≥10,000 copies/ml, a BK viral load reduction of ≥1 log₁₀ copies/ml was seen in 75% of participants being infused on a more frequent dosing schedule (group 1: bi-weekly) (six of eight), 63% (five of eight) of those in the monthly (group 2) dosing group, and 25% (one of four) in the placebo group (median BK viral load reduction −1.4 log₁₀ copies/ml [range, −2.1 to 0.1], −1.5 log₁₀ copies/ml [−1.8 to −0.2], and −0.4 log₁₀ copies/ml [−2.08 to −0.01], respectively) (Table 3 and Supplemental Figure 2).

Consensus groups use BK viremia of ≥10,000 copies/ml as a noninvasive marker for presumptive BK virus–associated nephropathy.^6,19 However, clinicians often start decreasing immunosuppression before BK viremia reaches values of 10,000 copies/ml, with many nephrologists decreasing immunosuppression when BK viremia reaches levels around 5000 copies/ml. Thus, we also evaluated the treatment effect of posoleucel in participants with BK viremia ≥5000 copies/ml who were within 2 years after kidney transplantation with stable immunosuppression before randomization. A BK viral load reduction of ≥1 log₁₀ copies/ml was seen in 73% of group 1 (more frequent dosing) participants (eight of 11), 50% (three of six) of group 2 (less frequent dosing) participants, and 17% (one of six) in the placebo group (median BK viral load reduction −1.3 log₁₀ copies/ml [range, −2.1 to 0.1], −1.1 log₁₀ copies/ml [−1.8 to 0.3], and −0.15 log₁₀ copies/ml [−2.1 to 0.2], respectively) (Table 3). The antiviral benefit of posoleucel was progressive over time (Figure 2 and Supplemental Figure 3).

Figure 2.

The antiviral response to posoleucel at weeks 14 and 24. (A) BK viral load at screening for all participants by low (350 to >10,000 copies/ml) and high (≥10,000–10,000,000 copies/ml) viral load strata and treatment group (PBO versus posoleucel). Median and min to max values indicated, with all data points shown. Percentage of participants that achieved ≥1 log₁₀ (B) or ≥50% (C) BK viral load reduction by week 14 (PBO, N=5; group 1, N=8; group 2, N=8) and week 24 (PBO, N=4; group 1, N=8; group 2, N=8) in the high viral load stratum (≥10,000–10,000,000 copies/ml), stable IS subpopulation. (D) Median log₁₀ change in BK viral load from baseline by week 14 (PBO, N=5; group 1, N=8; group 2, N=8) and week 24 (PBO, N=4; group 1, N=8; group 2, N=8) in the high viral load stratum (≥10,000–10,000,000 copies/ml), stable IS subpopulation. Stable IS: <50% IS reduction within 30 (±2) days before randomization. BKV, BK virus; PBO, placebo; PSL, posoleucel.

Other Outcomes: BK Virus T-Cell Function and Posoleucel Persistence

The frequency and functional capacity of BK virus–specific immunity was assessed by IFNγ ELISpot of preinfusion and postinfusion peripheral blood mononuclear cells following stimulation with BK virus peptides spanning large T and VP1 antigens to measure host-derived and posoleucel-derived virus–specific T-cell responses. VP1-reactive and large T-reactive IFNγ-producing T cells were evaluated in participants who completed the study (N=58/61) and are presented (1) by BK viral load strata (low stratum: 350 to >10,000 copies/ml; high stratum: ≥10,000–10,000,000 copies/ml), (2) by treatment arm (placebo, bi-weekly posoleucel, and monthly posoleucel), and (3) restricted to participants whose immunosuppression was stable before dosing (<50% immunosuppression reduction within 30 [±2] days before randomization).

At baseline (i.e., before dosing), most participants did not have detectable functional immunity (defined as spot-forming cell ≥10) to BK virus (n=42/58, 72%). Of those with functional responses (n=16), most (12/16, 75%; Figure 3A) participants were in the low viral load stratum, underscoring the importance of cellular immunity in BK virus control. Changes in BK virus functional immunity during the dosing and follow-up periods of the study were assessed. Participants who received more frequent posoleucel dosing had larger increases in functional BK virus–specific T cells by week 24 versus participants who received placebo (median fold change was 2.0 in the placebo group [n=18], 4.0 in group 1 [bi-weekly dosing; n=20], and 1.9 in group 2 [monthly dosing; n=20]; Figure 3B). Given that baseline functional BK virus–specific T cells were present in some study participants, subgroup analyses were performed by viral load strata, which revealed that posoleucel infusions resulted in larger increases in functional BK virus T cells by week 24 compared with placebo, and more frequent dosing produced larger effects (Figure 3C and Supplemental Figure 4). These effects were present in both strata but were more pronounced in the high BK viral load stratum with stable immunosuppression before randomization (median fold change was 0.5 in the placebo group [n=4], 3.8 in group 1 [n=8], and 2.1 in group 2 [n=8] [Figure 3C]). Analyses of cumulative BK virus ELISpot responses over time from week 2–6, week 2–14, and week 2–24 revealed that posoleucel recipients in the stable immunosuppression subgroup, high BK viral load stratum exhibited a progressive increase in the mean frequency of functional BK virus T cells, over time (Figure 3D), which was associated with a coincident reduction in viral load (Table 3).

Figure 3.

Effect of posoleucel on functional BK virus–specific T-cell responses. Posoleucel enhances functional BK virus–specific T-cell responses. (A) VP1 and large T IFNγ ELISpot SFC per 5×10⁵ PBMCs shown before posoleucel or placebo dosing as peak ELISpot response at screening or baseline for all participants who completed the study (N=58) in low (N=33; 350 to >10,000 copies/ml) and high (N=25; ≥10,000–10,000,000 copies/ml) viral load strata. Detectable functional BK virus T-cell responses defined as ≥10 SFC. Data graphed as box plots with median indicated and all data points plotted. (B) VP1 and large T-IFN-γ ELISpot data shown as fold change of peak ELISpot response from week 2–24 versus predose (with a minimum of five BK virus–specific SFC set as a predose response threshold) in all participants who completed the study (N=58). Data graphed as box plots with median indicated and all data points plotted. PBO, n=18; group 1, n=20; group 2, n=20. (C) VP1 and large T IFN-γ ELISpot data shown as fold change of peak ELISpot response from week 2–24 versus predose (with a minimum of five BK virus–specific SFC set as a predose response threshold) in high viral load stratum stable IS subgroup participants who completed the study (n=20). Data graphed as box plots with median indicated and all data points plotted. PBO, n=4; group 1, n=8; group 2, n=8. (D) VP1 and large T IFN-γ ELISpot data shown as fold change of peak ELISpot response from week 2–6, week 2–14, and week 2–24 versus predose (with a minimum of five BK virus–specific SFC set as a predose response threshold) in high viral load stratum stable IS subgroup participants who completed the study (n=4 PBO, n=16 posoleucel). The mean fold change is shown plus and minus the SEM. (E) The percentage of participants with detectable posoleucel T-cell clones is plotted relative to study week. Week 1 represents TCRvβ immunosequencing data collected before posoleucel infusion. The number of participants with evaluable data in the study week time period shown is indicated. (F) TCRvβ sum frequencies of posoleucel T-cell clones during week 4–6, 12–16, and 22–24 are plotted by viral load strata (low stratum n=19; high stratum week 4–6 n=15, week 12–24 n=16). Truncated violin plots shown with median and quartiles indicated by solid and dashed lines, respectively. Stable IS: <50% IS reduction within 30 (±2) days before randomization. ELISpot, enzyme-linked immunosorbent spot; PBMC, peripheral blood mononuclear cell; PBO, placebo; SFC, spot-forming cells; TCRvβ, T-cell receptor variable β.

To evaluate the presence and persistence of posoleucel, tracking studies were performed using TCRvβ deep sequencing with specific focus on detecting sequences that were unique to the infused posoleucel cell lines. All participants evaluated by TCRvβ sequencing (100%, n=35 with evaluable samples) had detectable posoleucel-derived T-cell clones at one or more time points during the dosing period (week 1–12) with persistence for up to 12 weeks after the dosing period in 100% of evaluable participants (n=35; Figure 3E). Of note, the sum median frequency of posoleucel-derived clones was consistently higher in the high versus low BK viral load stratum, suggesting a relationship between in vivo immune stimulation (i.e., viral load) and posoleucel frequency (Figure 3F: week 4–24; low viral load stratum median frequency range: 1.25×10⁻⁴ to 1.67×10⁻⁴, n=19; high viral load stratum median frequency range: 2.36×10⁻⁴ to 3.03×10⁻⁴, week 4–6 n=15, week 12–24 n=16).

Given the increased frequencies of VP1-reactive and large T-reactive functional T cells as well as posoleucel-derived T-cell clones in the high viral load stratum, the potential beneficial effect of posoleucel treatment on the emergence of endogenous BK virus–specific functional immunity was also evaluated. To assess host immunity after posoleucel intervention, an IFNγ ELISpot assay was used to assess the circulating frequency of smT-specific BK virus T cells, which revealed the presence of reactive cells and at higher frequencies by week 24 compared with placebo, for the stable immunosuppression subgroup, high BK viral load stratum (Supplemental Figure 5).

Discussion

In this blinded, phase 2 randomized study in kidney transplant recipients with BK viremia, repetitive infusion of the third party cell therapy posoleucel proved safe, with rates of AEs and treatment-related safety events similar among posoleucel and placebo groups. There were no deaths, no cases of CRS, or GVHD in any group, and no rejection events attributed to posoleucel treatment. Furthermore, the rates of de novo DSAs were low across both placebo and posoleucel groups. In addition, participants at high risk for disease progression that received posoleucel had reductions in plasma BK viral load that were coincident with improved BK virus functional immunity.

A serious unmet medical need exists for kidney transplant recipients who develop BK viremia to improve kidney outcomes. While many complex factors can contribute to allograft failure, multiple studies have shown a strong correlation between BK viremia, BK virus–associated nephropathy, and kidney allograft failure, including BK viremia at high levels as an independent risk factor for graft failure.²⁰ There are no approved treatments for BK virus infection. The drugs that are most often used off-label to treat BK virus infection, leflunomide and cidofovir, have not shown clear antiviral benefit and moreover are associated with toxicities.²¹ Studies on the use of intravenous immune globulin to treat BK virus infection have shown mixed results and have not identified a clear benefit.²² The current standard of care for kidney transplant recipients with BK virus infection, reduction of immunosuppression to allow the individual's own immune response to combat the virus, can result in BK viral load reduction, but this benefit brings with it a higher risk of graft rejection and the production of DSAs.²³ With no approved therapies for BK virus infection after kidney transplant, limitations in standard of care, lower graft survival, along with greater morbidity and higher associated health care costs, BK virus disease progression in transplant recipients remains a serious unmet medical need.²⁴

Posoleucel aims to address the underlying T-cell deficit associated with BK viremia in kidney transplant recipients by providing participants with ex vivo, activated, polyclonal, and polyfunctional BK virus–specific T cells to control BK virus infection. High-risk participants most in need of intervention (i.e., those with high viral loads and minimal endogenous BK virus T-cell reactivity) who received posoleucel exhibited enhanced functional BK virus–specific T-cell immunity postinfusion. Increased BK virus T-cell immunity was correlated with larger progressive BK viremia declines in posoleucel versus placebo recipients. To evaluate and track unique posoleucel clones during the study, T-cell receptor sequencing was used and confirmed the presence and persistence of posoleucel T cells during dosing and follow-up. In addition, there were greater sum frequencies of posoleucel-derived clones in participants in the high versus low viral load stratum, suggesting that in vivo T-cell levels were associated with magnitude of antigenic stimulation. Posoleucel recipients also showed evidence of endogenous immune activation subsequent to dosing, with the emergence of host-derived smT BK virus–specific T-cell responses. It is possible that posoleucel facilitated native BK virus–specific T-cell immune reconstitution, which can be dysfunctional in kidney transplant recipients.^25–27

Interpretation of the results of this study is limited by its small sample size, lack of long-term outcome data, and predominantly male population. In addition, each posoleucel infusion requires participants travel to an infusion center or clinic for administration, which can be burdensome.

This proof-of-concept study in kidney transplant recipients was designed to assess safety and tolerability and not the efficacy of posoleucel for the treatment of BK virus infection. However, the results suggest that posoleucel has an antiviral effect, which was most evident in participants with the highest levels of BK viremia, who are known to have a higher risk of nephropathy. However, larger phase 3 trials will be required for definitive efficacy and safety assessments.

In conclusion, in this exploratory study, posoleucel was generally safe and well tolerated with a safety profile consistent with that observed in hematopoietic stem cell transplant recipients.²⁸ Posoleucel appeared to be associated with antiviral effects in kidney transplant participants with BK viremia, for whom there are no currently approved therapies. The greatest BK viral load reduction was seen in participants with higher viral loads at baseline and in the group with more frequent posoleucel dosing. The reduction in BK viral load was associated with an increase in the circulating frequency of BK virus IFNγ⁺ T cells. Limitations of this study include the relatively small sample size and consequent lack of power to detect significant clinical effects as well as the short duration of follow-up. Nevertheless, these results support the investigation of posoleucel in a larger study to further evaluate its utility for the treatment of BK viremia in kidney transplant recipients.

Supplementary Material

jasn-35-618-s001.pdf ^{(720.4KB, pdf)}

Disclosures

D. Adey reports research funding from AlloVir, Hansa Pharmaceuticals, and Natera and honoraria from American Board of Internal Medicine. D. Adey reports advisory or leadership roles for American Society of Transplantation, OPTN/UNOS Policy Committee, Conflict of Interest Committee; Awards Committee; American Board of Internal Medicine, Subspecialty Governance Board; and Transplant International Editorial Board. T. Alhamad reports consultancy for CareDx, Natera, and Veloxis; research funding from AlloVir, Angion, CareDx, CSL Imagine, Eldon, Europhines, and Natera; honoraria from CareDx, Sanofi, and Veloxis; advisory or leadership role for CareDx, Europhines, Horizon, and QSANT; Advisory Boards for ANI, CareDx, Eurofins, Horizon, and Nateria; clinical trials supported by AlloVir, CSL Behring, Eldon, Memo Therapeutics, and NIH; and speakers bureau for CareDx, Sanofi, and Veloxis. A. Alper reports research funding from AlloVir. M.J. Ansari reports research funding from AlloVir, Eurofins/Transplant Genomics, and Verici Dx; honoraria from AlloVir; patents or royalties from Tract Therapeutics; and advisory or leadership role for AlloVir. F. Cardarelli reports employment with AlloVir, Beth Israel Deaconess Medical Center, and Brigham and Women Hospital; consultancy for Natera; stock in AlloVir; patents or royalties from AlloVir; and other interests or relationships as an AST member. A. Chandraker reports consultancy for AlloVir, Chinook, Egenesis, Immucor, Natera, Mitobridge, Sanofi, and Shire; research funding from AlloVir, Amgen, CSL, Hansa, and Natera; honoraria from Natera; patents or royalties from Anya Therapeutics; advisory or leadership role for American Society of Transplantation as Development Chair of Transplant Therapeutics Consortium and Scientific/Medical Advisory Board Member for Orthogon; and other interests or relationships with Anya Therapeutics as Founder and Scientific Advisor. L.-X. Chen reports research funding from AlloVir, Astellas, CSL Behring, Dexcom, Memo Therapeutics, Transplant Genomics, TruGraf, and Veloxis. D. Cibrik reports consultancy for CareDx and Eledon and role as scientific advisor for Calliditas, CareDx, Eledon, and Sanofi. D.M. Dadhania reports consultancy for AlloVir Inc. Advisory Board and CareDx; research funding from AlloVir, CareDx, CSL Behring, Memo Therapeutics, and NIH; inventor on patent application W02018187521A2 titled “Methods of Detecting Cell-Free DNA in Biological Samples,” licensed to Eurofins; clinical trials supported by AlloVir, CSL Behring, and Memo Therapeutics; and advisory or leadership roles as an AST Committee member, Associate Editor of Transplantation, member of CareDx Advisory Board, member of LiveOnNY Medical Advisory Board, and Section Editor for Nephrology Dialysis Transplantation. A. Faravardeh reports employment with SHARP Kidney and Pancreas Transplant Center, consultancy for Natera and Veloxis, research funding from CareDx and Natera, honoraria from Natera and Veloxis, and speakers bureau for Natera and Veloxis. D. Florescu reports consultancy from Merck, Medpace, and Takeda and research funding from AlloVir, Bavarian Nordic, Merck, Nobelpharma, Novavax, Regeneron, SymBio, and Takeda. S. Gilmore reports employment with AlloVir, Genentech, and Gilead; ownership interest in AlloVir, Genentech, and Gilead; and patents or royalties from UC Berkeley. R. Gohh reports employment with Brown Physicians, Inc.; research funding from AlloVir, CareDx, Regeneron, United Therapeutics, Valenza, and Vertex; advisory or leadership roles for AST Elections Committee, AST IDEAL Committee (past-Chairperson), Transplantation Editorial Board, UNOS Board of Directors, and UNOS Region 1 Administrator; and speakers bureau for CareDx and Veloxis. G. Gupta reports consultancy for CareDx; research funding from Merck Pharmaceuticals; honoraria from Alexion, CareDx, Mallinckrodt, Natera, and Veloxis; advisory or leadership role for Frontiers of Medicine; speakers bureau for Alexion, CareDx, Mallinckrodt, and Veloxis; Scientific Advisory Board for CareDx; and other interests or relationships with AST KPOP Executive Committee, AST Transplant Nephrology Fellowship Accreditation Committee, and National Kidney Foundation Virginia. D. Jain reports CareDx industry-sponsored research and other interests or relationships as a member on the National Kidney Foundation of Illinois Board of Directors since January 2018 and National Kidney Foundation as a Transplant Advisory Committee member. D. Jain's spouse reports employment with United Health Care. S. Knechtle reports consultancy for CSL Behring, Hansa, and Viterras; research funding from Alexion and CSL Behring; honoraria from Alexion; and patents or royalties from Renovar. B.E. Lonze reports research funding from Abbvie, AlloVir, CareDx, Hansa, and NIH-NAIAD (R34AI177209); consultancy for ArgenX and Hansa Biopharma; honoraria from Physicians' Education Resource®, LLC (PER); and advisory or leadership role for Argenx. J. Ma reports employment with and stock in AlloVir. V. Nair reports employment with Northwell Health. S. Norman reports employment with University of Michigan Health Systems; research funding from AlloVir and Natera; advisory or leadership role for Board of Directors, American Kidney Fund Board of Trustees, MOTTEP Detroit Foundation Board, National Kidney Foundation of Michigan Scientific Advisory Board, and OPTN/UNOS Board of Directors; and other interests or relationships with Mitzvah Circle Foundation. A. Regmi reports research funding from Eurofin-TRULO study. A.P. Rossi reports employment with Piedmont Transplant Institute. A. Sharfuddin reports royalties from UpToDate. A. Sharma reports the ownership interest in Amazon and Berkshire Hatahway. M. Singh reports research funding from AlloVir trial, Bestow Trial, and Imagine Trial and clinical trials supported by AlloVir, CSL Behring, and Eledon Pharmaceutical. S. Vasileiou reports consultancy for and research funding from AlloVir Inc. D. Wojciechowski reports consultancy from AlloVir, CareDx, eGenesis, and Natera; research funding from AlloVir, CareDx, Natera, Novartis, and VielaBio; honoraria from AlloVir, CareDx, Natera, and Novartis; and advisory or leadership role for eGenesis, Natera, and Novartis. E.S. Woodle reports employment with University of Cincinnati; consultancy for Novartis and Sanofi; research funding from Amgen, Bristol Myers Squibb, Novartis, and Veloxis; and honoraria from Novartis and Sanofi. University of Cincinnati owns a patent on E.S. Woodle's behalf that is not yet licensed. J.-A.H. Young reports research funding from AlloVir, Ansun, Cidara, F2G, GSK, Pulmocide, Scynexis, Takeda, and Zepto; research reimbursement from AlloVir for participants enrolled in this trial; and advisory or leadership role for AlloVir. Z. Zaky reports employment with Cleveland Clinic. The remaining author has nothing to disclose.

Funding

AlloVir, Inc.

Author Contributions

Conceptualization: Francesca Cardarelli.

Data curation: Julie Ma.

Formal analysis: Sarah Gilmore, Peter T. Jindra, Julie Ma, Spyridoula Vasileiou.

Investigation: Deborah Adey, Tarek Alhamed, Arnold Alper, Mohammed J. Ansari, Anil Chandraker, Ling-Xin Chen, Diane Cibrik, Darshana M. Dadhania, Arman Faravardeh, Diana Florescu, Reginald Gohh, Guarav Gupta, Divya Jain, Stuart Knechtle, Bonnie E. Lonze, Vinay Nair, Silas Norman, Anil Regmi, Ana P. Rossi, Asif Sharfuddin, Akhil Sharma, Manpreet Singh, David Wojciechowski, E. Steve Woodle, Jo-Anne H. Young, Ziad Zaky.

Methodology: Francesca Cardarelli, Anil Chandraker, Sarah Gilmore, Julie Ma, Spyridoula Vasileiou.

Project administration: Francesca Cardarelli.

Supervision: Francesca Cardarelli, Anil Chandraker.

Validation: Julie Ma.

Writing – original draft: Sarah Gilmore.

Writing – review & editing: Deborah Adey, Tarek Alhamed, Arnold Alper, Mohammed J. Ansari, Francesca Cardarelli, Anil Chandraker, Ling-Xin Chen, Diane Cibrik, Darshana M. Dadhania, Arman Faravardeh, Sarah Gilmore, Reginald Gohh, Guarav Gupta, Divya Jain, Peter T. Jindra, Stuart Knechtle, Bonnie E. Lonze, Julie Ma, Vinay Nair, Silas Norman, Anil Regmi, Ana P. Rossi, Asif Sharfuddin, Akhil Sharma, Manpreet Singh, Spyridoula Vasileiou, David Wojciechowski, E. Steve Woodle, Jo-Anne H. Young, Ziad Zaky.

Data Sharing Statement

Qualified researchers may request from AlloVir data supporting the clinical findings of this study by contacting info@allovir.com. Individual patient data will not be shared.

Supplemental Material

This article contains the following supplemental material online at http://links.lww.com/JSN/E601.

Supplemental Table 1. Demographics and disease characteristics of participants without immunosuppression reduction.

Supplemental Table 2. Participants who had immunosuppression reduction before randomization.

Supplemental Table 3. Change in eGFR from baseline, ml/min per 1.73 m².

Supplemental Figure 1. Schema for immunosuppression modification.

Supplemental Figure 2. Median and per participant BK viral load log10 change from baseline.

Supplemental Figure 3. Time to first BK viral load ≥1 log10 decline.

Supplemental Figure 4. ELISpot response from week 2–24 versus predose in participants with stable immunosuppression: low viral load stratum.

Supplemental Figure 5. Small T ELISpot response from week 2–24 versus predose in participants with stable immunosuppression: high viral load stratum.