CITN-12: Pembrolizumab in HIV-associated Kaposi Sarcoma

Abstract

PURPOSE:

Cancer Immunotherapy Trials Network 12 (CITN-12) demonstrated safety of pembrolizumab in treating advanced cancer in people with HIV. Here we report results of the Kaposi sarcoma (KS) cohort.

PARTICIPANTS AND METHODS:

In this multicenter phase 1 trial we enrolled participants with HIV-associated KS on antiretroviral therapy with CD4⁺ ≥50 cells/μL and HIV plasma RNA <200 copies/mL. Pembrolizumab 200 mg IV was administered every 3 weeks for up to 35 cycles. The primary endpoint was safety, and the secondary endpoint was KS response by modified AIDS Clinical Trials Group Criteria.

RESULTS:

Thirty-two cisgender men enrolled with baseline median CD4⁺ T-cell count of 274 cells/μL. All but 9 participants had received prior systemic KS therapy. Participants received a median of 11 cycles of pembrolizumab (range, 1-35). Sixty-six percent had grade ≥1 treatment-emergent adverse events (TEAEs), including 1 death from polyclonal Kaposi sarcoma herpesvirus-related B-cell lymphoproliferation. Thirty-one percent had ≥1 immune-mediated AEs (imAEs) with 25% requiring systemic steroids. In 29 participants with evaluable KS, the overall response rate (ORR) was 62.1% (95% CI, 42.3-79.3) and did not differ by CD4⁺ T-cell count. ORR in the 8 participants with evaluable disease without prior KS therapy was 87.5% (95% CI, 47.3-99.7). Median duration of response (DOR) was not reached, and the Kaplan-Meier estimate of DOR of ≥12 months was 92.3% (95% CI, 56.6-98.8). Median progression-free survival was 28.2 months (95% CI, 4.2-non-calculable).

CONCLUSIONS:

Pembrolizumab yielded a high rate of durable responses in HIV-associated KS. imAEs were successfully managed with standard guidelines.

Clinicaltrials.gov number NCT02595866.

Introduction

Kaposi sarcoma (KS) is a multicentric endothelial cancer caused by Kaposi sarcoma herpesvirus (KSHV), also known as human herpesvirus 8, most commonly affecting people with HIV (PWH).¹ It is strongly associated with CD4⁺ T-cell lymphopenia; however, there remains an unmet need for effective treatment of HIV-associated KS in patients with well-controlled HIV at higher CD4⁺ T-cell counts.² Antiretroviral therapy (ART) has decreased the incidence of KS worldwide, but rates have not declined among Black men in the southeastern United States, and KS remains the most common cancer among men less than 65 years of age in several countries in sub-Saharan Africa.^3,4 KS is the most common cancer affecting adolescent and young adult men and women with HIV in South Africa.⁵ The United States Food and Drug Administration (FDA) has approved two chemotherapy agents, liposomal doxorubicin and paclitaxel, and the immunomodulatory agent, pomalidomide, for HIV-associated KS. While response rates range from 46-76% with these agents, patients often require intermittent KS therapy throughout their lifetime, leading to repeated exposure to these agents known to cause cumulative toxicities.^6–12 Repeated exposure to cytotoxic chemotherapy may hamper immune reconstitution, and thereby increase the risk of opportunistic infections and other cancers.^13,14

T-cell dysfunction in HIV-associated KS is related to HIV-related CD4⁺ T-cell loss and among patients on ART, increased proportions of CD57⁺ senescent T-cells.^15,16 Chronic T-cell stimulation from HIV and KSHV leads to up-regulation of immune checkpoint molecules, such as programmed death protein 1 (PD-1), loss of cytotoxic CD8⁺ T-cell responses, and T-cell exhaustion.^17–20 PD-1 ligand (PD-L1), which may be upregulated on tumor cells and antigen presenting cells, is expressed in 70% of HIV-associated KS cases, but largely in the tumor microenvironment.^21,22 PD-1 pathway upregulation in macrophages and natural killer cells has also been implicated in HIV-associated KS.^23,24 ART improves CD4⁺ T-cell counts and T-cell function over time, but evidence of HIV-related immune dysregulation, including higher expression of PD-1, continues even with long-term ART and irrespective of CD4⁺ T-cell count.²⁵ Anti-PD-1 agents, such as pembrolizumab, block the inhibitory signal transmitted when PD-1 binds to PD-L1, allowing for improved immune surveillance and cytotoxic killing of cancer cells. Additionally, anti-PD-1 agents may enhance priming or expansion of T-cells and promote CD4⁺ T-cell diversity, which further promote anti-tumor activity.^26,27 Anti-PD1 agents are appealing in PWH because they are not immunosuppressive and may reverse HIV-induced T-cell dysfunction. Anti-PD-1 agents are FDA-approved for many HIV-associated cancers, yet PWH were excluded from most trials that led to FDA approvals.²⁸ Cancer Immunotherapy Trials Network 12 (CITN-12) demonstrated the safety of pembrolizumab in participants with ≥100 CD4⁺ T-cells/μL in participants with controlled HIV on ART who had a variety of advanced cancers.²⁹ CITN-12 was expanded to include a cohort of participants with KS, and here we report the results of all participants with KS.

Methods

Study design and treatment

CITN-12 is an investigator-initiated multicenter phase 1 trial (Appendix 1). Participants were recruited at 8 centers in the United States and received pembrolizumab 200 mg intravenously every 3 weeks for up to 35 cycles or 2 years of treatment. Participants with symptomatic HIV-associated KS receiving ART for >3 months with a plasma HIV RNA <200 copies/mL were eligible.³⁰ Participants with symptomatic pulmonary KS, platelets less than the lower limit of normal, hemoglobin ≤10 g/dL, and ECOG ≥2 were excluded. Baseline evaluation required a chest x-ray to investigate for asymptomatic pulmonary lesions and assessment for occult blood loss, gastrointestinal infections, and endoscopy and in those with gastrointestinal symptoms or microcytic anemia.

The first published portion of the trial demonstrated the safety of pembrolizumab in participants enrolled into CD4⁺ T-cell count cohorts (cohort 1: 100-200, cohort 2: 201-350, cohort 3: >350 cells/μL). Subsequent protocol amendments included the KS cohort allowing for participants who had not received prior KS therapy, reduced the CD4⁺ T-cell count for enrollment from 100 cells/μL to ≥50 cells/μL, and excluded participants with active KSHV-associated multicentric Castleman disease (MCD) in the past 5 years. No changes were made to the dosing or schedule of pembrolizumab administration.

Response to treatment was evaluated every odd cycle by modified AIDS Clinical Trials Group (ACTG) KS response criteria.^30,31 CD4⁺ T-cell count and plasma HIV viral load were measured every cycle for the first 4 cycles and every other cycle thereafter. The primary endpoint was the safety of pembrolizumab for relapsed/refractory KS and as first systemic therapy for KS in participants with HIV on ART evaluated by National Cancer Institute Common Terminology Criteria for Adverse Events. The secondary endpoint was the overall response rate (ORR) of pembrolizumab in HIV-associated KS in those with and without prior systemic KS therapy.

Study Oversight

CITN-12 was coordinated by the CITN and sponsored by the National Cancer Institute Cancer Therapy Evaluation Program. The study was approved by the Institutional Review Boards at Fred Hutchinson Cancer Center and participating sites. The study was conducted in accordance with the Declaration of Helsinki, and all participants provided written informed consent.

KSHV assessments

As part of safety assessment, peripheral blood mononuclear cell (PBMC)-associated KSHV viral loads were measured on cryo-preserved PMBC collected at baseline, cycle 1 day 8, cycle 4 day 1, and end-of-treatment using previously described methods.³² For correlative evaluation of KSHV-specific T-cell responses, cryo-preserved PMBC collected at baseline and cycle 4 day 1 were evaluated via a whole KSHV proteome interferon-gamma ELISpot assay employing ~7,500 overlapping 15mer peptides into peptide pools for 83 KSHV open reading frames (ORFs), with responses considered positive if >60 spot-forming units (sfu)/10⁶ cells.^33,34 Breadth of T-cell responses was determined by the number of antigens eliciting interferon-gamma responses and intensity of responses was determined by sfu/10⁶ cells.

Statistical Analysis

Safety analyses were based on participants with KS enrolled into any cohort who received at least 1 dose of pembrolizumab. Efficacy analyses were based on participants with KS evaluable by modified ACTG criteria, which requires the identification of ≥5 bi-directionally measurable KS cutaneous marker lesions. Analyses included 8 participants with KS from the original 3 cohorts previously published.²⁹ Changes in CD4⁺ T-cell counts and KSHV viral loads were evaluated by one-sample Wilcoxon signed-rank tests. Comparisons of ORR by CD4⁺ T-cell count and prior therapy were evaluated by Fisher’s exact method. Changes in the breadth and intensity of KSHV-specific T-cell responses were evaluated by two-sample t-tests. Progression-free survival (PFS) and duration of response (DOR) were evaluated by Kaplan-Meier methodology. Comparisons of PFS, OS, and TTR by CD4⁺ T-cell count and prior KS therapy were calculated by log-rank tests. The median time to the first observed treatment response (TTR) was calculated from the first dose of pembrolizumab to the initial KS response that was subsequently confirmed via investigator assessment. PFS was determined by the time from the first dose of pembrolizumab to progressive disease or death. Participants without treatment responses, progressive disease or death were censored at the last disease assessment date. The data cut-off for analysis was June 20, 2023.

Results

Participants and treatment

From April 2016 through March 2023, 32 cisgender men with KS were enrolled, 8 in cohorts 1-3, and 24 in cohort 4 (Table 1 and Appendix Table 1). The median age was 45 years (range: 28-66); 15 (47%) were Black, 16 (50%) were White, and 1 (3%) with unreported race. Seven (22%) were Hispanic/Latino. The median CD4⁺ T-cell count was 274 cells/μL (range: 95-1030), and 11 participants had CD4⁺ T-cell counts <200 cells/μL. Twenty-six (81%) had advanced stage (T1) KS, and 2 participants from cohorts 1 and 2 had concurrent primary effusion lymphoma. Twenty-three (72%) participants had received prior systemic KS therapy (median=3; range: 1-12), and pembrolizumab was the first systemic therapy in 9 (28%) participants. The most common prior therapies were liposomal doxorubicin, paclitaxel, and pomalidomide. Participants received a median of 11 cycles of pembrolizumab (range: 1-35). Two participants completed 35 cycles or 2 years of treatment, and 6 participants had ongoing treatment at the time of data cut-off. Nine participants discontinued pembrolizumab due to progressive disease, 5 due to unacceptable toxicities, 3 refused further treatment, 1 participant died on treatment, and 6 discontinued for other reasons.

Table 1. Baseline participant and disease characteristics.

Participant characteristics	All participants	Participants with prior KS therapy	Participants without prior KS therapy*
Participants, n (%)	32 (100)	23 (72)	9 (28)
Age, years, median (range)	45 (28, 66)	43 (28, 61)	54 (38, 66)
Men, n (%)	32 (100)	23 (100)	9 (100)
Race
White, n (%)	16 (50)	11 (48)	5 (56)
Black, n (%)	15 (47)	12 (52)	3 (33)
Not specified, n (%)	1 (3)	0	1 (11)
Hispanic/Latino, n (%)	7 (22)	6 (26)	1 (11)
Disease characteristics
ACTG Tumor Stage
T1	26	21	5
T0	6	2	4
Number of prior systemic therapies, median (range)	3 (1, 12)	3 (1,12)	-
Prior radiation therapy, n (%)	10 (31)	8 (35)	2 (22)
HIV characteristics
CD4+ cells/μL, median (range)	274 (95, 1030)	228 (95, 979)	319 (101, 1030)
CD4+ 50-199 cells/μL, n (%)	11 (34)	8 (35)	3 (33)
CD4+ 200-350 cells/μL, n (%)	6 (19)	4 (17)	2 (22)
CD4+ >350 cells/μL, n (%)	15 (47)	11 (48)	4 (44)
CD4+/CD8+ ratio, median (range)	0.48 (0.13, 3.43)	0.48 (0.13, 1.88)	0.49 (0.15, 3.43)
CD4+/CD8+ ratio <1, n (%)	25 (78)	18 (78.3)	7 (78)
Detectable plasma HIV RNA ≥20 copies/mL, n	0	0	0
Opportunistic prophylaxis, n (%)	19 (59)	15 (65)	4 (44)

^*Participants received pembrolizumab as the first systemic KS treatment.

T1 indicates KS with associated lymphedema, nodular or extensive involvement of the oropharynx, or visceral disease.

T0 indicates KS limited to the skin or minimal involvement of the oropharynx.

ACTG indicates AIDS Clinical Trials Group; KS, Kaposi sarcoma.

Safety

All 32 participants with KS were included in the safety analysis. Twenty-one (66%) participants experienced at least one pembrolizumab-related treatment-emergent adverse event (TEAE). Most participants experienced grade 1 (25%) or grade 2 (22%) TEAE; however, 5 (16%) experienced grade 3 as the worst grade AE and one participant died due severe KSHV-associated polyclonal B-cell lymphoproliferation, as previously detailed (Appendix Table 2).²⁹ Five participants discontinued treatment due to unacceptable TEAE. Ten (31%) participants experienced immune-mediated adverse events (imAEs) with 8 (25%) participants requiring steroids and 2 (6%) requiring levothyroxine (Table 2). All imAEs were successfully managed according to protocol guidelines. One participant developed an exacerbation of biopsy-proven cytomegalovirus (CMV) enteritis and atypical mycobacterial mesenteric lymphadenitis after one cycle of treatment requiring pembrolizumab discontinuation. This participant had recently completed valganciclovir treatment with resolution of symptoms prior to enrollment, and details of the case have been previously reported.³⁵

Table 2. Immune-mediated Treatment Emergent Adverse Events (imAE) at Least Possibly Related to Pembrolizumab.

Toxicity Grade	CD4+ 50-199 cells/μL (n=11) n (%)	CD4+ 200-350 cells/μL (n=6) n (%)	CD4+ >350 cells/μL (n=15) n (%)	All participants (n=32) n (%)
Patients with ≥1 imAE
Any grade	1 (9.1)	3 (50)	6 (40)	10 (31.3)
Grade 1	0	0	1 (6.7)	1 (3.1)
Grade 2	1 (9.1)	2 (33.3)	2 (13.3)	5 (15.6)
Grade 3	0	1 (16.7)	3 (20)	4 (12.5)
Anemia
Grade 3	0	0	1 (6.7)	1 (3.1)
Colitis
Grade 3	0	0	1 (6.7)	1 (3.1)
Hypothyroidism
Grade 2	0	1 (16.7)	1 (6.7)	2 (6.3)
Cytomegalovirus infection reactivation
Grade 3	0	1 (16.7)	0	1 (3.1)
Mycobacterium avium complex
Grade 3	0	1 (16.7)	0	1 (3.1)
Blood bilirubin increased
Grade 2	1 (9.1)	0	1 (6.7)	2 (6.3)
Arthralgia
Grade 2	0	0	1 (6.7)	1 (3.1)
Pain in extremity
Grade 1	0	0	1 (6.7)	1 (3.1)
Grade 2	0	0	1 (6.7)	1 (3.1)
Pneumonitis
Grade 2	0	1 (16.7)	0	1 (3.1)
Grade 3	0	0	1 (6.7)	1 (3.1)
Maculo-papular rash
Grade 3	0	0	1 (6.7)	1 (3.1)
Skin hypopigmentation
Grade 1	0	0	1 (6.7)	1 (3.1)

imAE indicates immune-mediated treatment-emergent adverse event

The median CD4⁺ T-cell count increase from baseline to end-of-treatment was 53 cells/μL (P=0.048) (Appendix Table 3). Plasma HIV RNA remained <200 copies/mL in all participants throughout treatment. The median PBMC-associated KSHV viral load at baseline was 0 copies/10⁶ PBMC (interquartile range (IQR): 0-136) with no acute increases on cycle 1 day 8 (P=0.7). Eight participants had a detectable KSHV viral load at baseline (range: 421-77,333 copies/10⁶ cells), including 2 participants with concurrent PEL. Only 2 of these participants had detectable KSHV at the last measurement, including the participant who developed KSHV-associated polyclonal B-cell lymphoproliferation (range: 1556-388,235 copies/10⁶ cells). Only one participant with no detectable KSHV DNA copies at baseline had an asymptomatic detectable viral load at the final measurement (103 copies/10⁶ cells).

Efficacy and outcomes

Twenty-nine participants had evaluable KS. Three participants’ KS could not be evaluated for response: 1 who received only one cycle of pembrolizumab, and 2 who enrolled in cohorts 1 and 2 with primary effusion lymphoma and concurrent non-evaluable KS who were included in the safety analysis only. Among the 29 participants with evaluable KS, the ORR was 62.1% (95% confidence interval (CI): 42.3, 79.3) (Figure 1, Appendix Table 4). The ORR was 87.5% (95% CI: 47.3-99.7) among the 8 participants who received pembrolizumab as first-line systemic KS therapy versus 52.4% (95% CI: 29.8-74.3) among the 21 participants who received pembrolizumab as second-line or greater therapy (P=0.08). There was no difference in ORR by CD4⁺ T-cell count (P=0.77). Eighteen participants had a partial response, 8 had stable disease, and 3 had progressive disease as the best overall response. Among those with a partial response, the median TTR was 2.9 months (IQR: 1.5-8.3) and did not differ by CD4⁺ T-cell count (P=0.79) or by whether pembrolizumab was received as first-line therapy (P=0.43). With median follow-up time of 5.8 months (95% CI: 3.3-14.1), the median DOR was not reached (range=1.4-21.7 months), and the Kaplan-Meier estimate of a DOR of ≥12 months was 92.3% (95% CI: 56.6-98.9) (Figure 2). The PFS among participants with evaluable KS was 28.2 months (95% CI: 4.2-not calculable) with median follow-up time of 13.4 months (95% CI: 7.4-18.9). PFS did not differ by CD4⁺ T-cell count or by whether pembrolizumab was received as first-line therapy (P=0.58; P=0.27, respectively) (Figure 2). The median OS among all 32 participants was not reached (95% CI: 17.2-non-calculable) and did not differ by CD4⁺ T-cell count or prior therapy (P= 0.63; P=0.29, respectively).

Figure 1. Regression of cutaneous Kaposi sarcoma in 2 participants after treatment with pembrolizumab.

Modified AIDS Clinical Trials Group Criteria for Kaposi sarcoma assessment of cutaneous lesions includes measures of the total number of lesions, number of nodular lesions, and sum of the area of five marker lesions. When more than 50 lesions are present, a representative area of the body is identified, and lesions are counted and measured only within this area. Panel A shows photos of the right lower extremity of a 33-year-old participant with baseline CD4⁺ T cell count of 526 cells/μL and T1 Kaposi sarcoma (KS) involving the lungs and skin previously treated with liposomal doxorubicin, pomalidomide, and paclitaxel. Panel B shows a reduction in the number of lesions in the right lower extremity after 4 cycles of pembrolizumab. Panel C shows the percent change from baseline in total number of lesions, number of nodular lesions, total area of the five marker lesions, CD4⁺ T-cell counts, and CD8⁺ T-cell counts with pembrolizumab treatment. At baseline, the participant had more than 50 lesions and a representative area on the arms and legs was identified. Within the representative area, 28 total lesions, 9 nodular lesions, and five marker lesions with total area of 760 mm³ were identified. At cycle 13 day 1, the total number of lesions had reduced to 10 and the total area had reduced to 480 mm³. Panels D and E show photos of the plantar surface of the feet of a 53-year-old man with baseline CD4⁺ T cell count of 169 cells/μL and T1 KS previously treated with liposomal doxorubicin, paclitaxel, and pomalidomide. Panels E and F show the same participant’s feet with a reduction in the number and nodularity of the cutaneous KS lesions after 8 cycles of pembrolizumab. Panel H shows the percent change from baseline of the total number of lesions, number of nodular lesions, total area of the 5 marker lesions, and CD4⁺ and CD8⁺ T-cell counts. At baseline, the participant had more than 50 lesions and a representative area on the arms and torso was identified. Within the representative area, 27 total lesions, 18 nodular lesions, and five marker lesions with total area of 2250 mm³ were identified. At cycle 9 day 1, the total number of lesions had reduced to 11 and there were zero nodular lesions in the representative area.

Figure 2. Kaposi sarcoma responses and progression-free survival.

Panel A shows a swimmer’s plot of participant responses. Each bar represents one participant, blue circles indicate time of partial response which is plotted until progressive disease or the last KS response assessment, whichever occurred later. Arrows indicate ongoing partial response at the time of data cut-off. The darker gray indicates the duration of response. Panel B shows the progression-free survival in all participants with response evaluable Kaposi sarcoma. Panel C shows the progression-free survival by CD4⁺ T-cell count, and Panel D shows the progression-free survival by pembrolizumab as first systemic KS therapy versus second-line or greater therapy.

KSHV-specific T-cell responses

KSHV-specific T-cell responses were evaluable in 19 participants at baseline and cycle 4 day 1 (Figure 3). Responses were heterogeneous with no shared immunodominance.³³ The median number of ORFs eliciting interferon-gamma responses was 5 (IQR: 3-8) at baseline and 4 (IQR: 1-6) at cycle 4 day 1. The most common ORFs eliciting responses were lytic proteins, including K8.1, a viral glycoprotein that elicits antibody responses used to measure KSHV seropositivity. There was no difference in the breadth or intensity (sfu/10⁶ cells) of T-cell responses in participants with a baseline CD4⁺ T-cell count <350 cells/μL versus those with CD4⁺ T-cell count >350 cells/μL at baseline or cycle 4 (baseline breadth/intensity P=0.33/P=0.51; cycle 4 breadth/intensity P=0.65/P=0.74). There was no difference in participants with a KS response versus those without a KS response (baseline breadth/intensity P=0.40/P=0.74; cycle 4 breadth/intensity P=0.28/P=0.82). Notably, the median breadth and intensity declined from baseline to cycle 4 in participants with KS responses (5.5 ORFs and 160 sfu/10⁶ cells at baseline versus 3.5 ORFs and 125 sfu/10⁶ at cycle 4). This effect was not observed in participants without a KS response (4 ORFs and 169 sfu/10⁶ cells at baseline versus 6 ORFs and 170 sfu/10⁶ at cycle 4).

Figure 3. Kaposi sarcoma herpesvirus (KSKV)-specific T-cell responses.

Heat map showing breath and intensity of KSHV-specific T-cell responses in 19 participants in whom interferon-gamma T-cell responses were evaluated using an ELIspot assay against 83 KSHV open reading frames (ORFs) at baseline and at cycle 4 day 1. Responses were measured in spot-forming units (sfu)/10⁶ cells. Each column represents one participant. Each row represents a KSHV ORF, which are organized according to their role in the KSHV life cycle.

Discussion

To our knowledge, this is the largest prospective study of anti-PD-1 therapy in HIV-associated KS. Pembrolizumab led to a high rate of durable KS responses in participants in whom ART had failed to adequately control their KS. The ORR of >60% is comparable to response rates observed in Hodgkin lymphoma where PD-1 blockade is highly effective and used in all lines of therapy.^36,37 In addition to the results from CITN-12 presented here, anti-PD-1 agents have previously demonstrated activity in KS. A phase 2 study of 17 participants with HIV-negative KS treated with pembrolizumab for up to 8 cycles demonstrated an ORR of 71%.³⁸ A phase 2 study of nivolumab plus low-dose ipilimumab, a cytotoxic T-lymphocyte antigen 4 inhibitor, treated 18 participants with previously treated HIV-negative KS for up to 24 months resulting in an ORR of 87%.³⁹ Participants with HIV-associated KS were also included in the AIDS Malignancy Consortium (AMC) 095 Study of the PD-1 inhibitor, nivolumab.⁴⁰ In 15 participants with previously treated HIV-associated KS and CD4⁺ T-cell counts ≥200 cells/μL who received up to 2 years of nivolumab, the ORR was 40% and the median DOR of 12.5 months.

Although indirect comparisons between KS treatments is limited by differences in patient-related factors and duration of treatment, the ORR of 62%, TTR of <3 months, and PFS of >28 months observed with pembrolizumab compare favorably to benchmarks from clinical trials of standard cytotoxic chemotherapies used in HIV-associated KS. Similar DOR was observed with only 6 months of pembrolizumab in HIV-negative KS.³⁸ Paclitaxel, the best studied agent in KS, has an ORR between 56-58% in the first-line and relapsed settings.^6,7,41 The median DOR of paclitaxel is 17.5 – 20 months in the first-line setting and 8.9 months in the recurrent setting. A limitation of older KS studies is that some patients had suboptimal HIV control and were on older antiretroviral regimens that may have drug-drug interactions with cytotoxic chemotherapy, however, pembrolizumab has no potential drug-drug interactions with ART.⁴² Pembrolizumab was particularly active in those with low CD4⁺ T-cell counts and CD4⁺ T-cell immune reconstitution was observed in these participants. Although ART is a critical component of HIV-associated KS treatment, there is little evidence that ART alone led to regression of advanced, symptomatic KS in our study given participants must have had inadequate KS control after >3 months of ART prior to enrollment.⁴³

We evaluated KSHV-specific immunity using a novel multiplex ELISPOT assay, which demonstrated that patients had polyclonal KSHV-specific immune responses that were inadequate for KS control. Participants with a KS response to pembrolizumab had a decline in KSHV-specific T-cell responses, akin to our previous findings that patients with KSHV-associated diseases have higher breadth and intensity of KSHV-specific T-cell responses compared with KSHV seropositive healthy controls, suggesting peripheral blood KSHV-specific T-cell interferon-gamma responses are also biomarker of KS burden.³³ This contrasts with one study that observed an increase in KSHV-specific T-cell responses against a limited number of KSHV antigens in ART naïve patients with HIV-associated KS after initiation of ART.⁴⁴ Further evaluation of timepoints proximal to the initiation of immune therapies (including ART) as well as tumor-infiltrating lymphocytes by multiplex ELISPOT are next steps to investigate the role of KSHV-specific T-cells in KS control.

Thirty-one percent of participants experienced imAEs, which were successfully managed with standard guidelines. Of note, there were fewer imAEs in participants with CD4⁺ T-cell counts <200 cells/μL compared with participants with higher CD4⁺ T-cell counts, a phenomenon also reported in a large, international retrospective trial of PWH and cancer who received anti-PD-1 agents.⁴⁵ A unique consideration of imAE management in KS is the association of prolonged courses of steroids and other immunosuppressive agents used to treat imAEs with possible progression of KS.⁴⁶ Studies of paclitaxel in HIV-associated KS report 46-84% of participants experienced grade ≥3 AEs.^6,7 Therefore, the relative risk of imAEs associated with anti-PD-1 therapy needs to be weighed against the cumulative risks and healthcare burden of neutropenia, anemia, serious infections, and neuropathy observed with cytotoxic chemotherapy.^7,47

Two participants had serious adverse events related to infectious agents, exacerbation of CMV and atypical mycobacterial infection in one participant and the previously described polyclonal KSHV-associated B-cell lymphoproliferation in another. Activation of CD4⁺ T-cells via PD-1 inhibition has been shown to promote rather than control mycobacteria at the infection site, and exacerbation of mycobacterial infections has been noted in patients without HIV receiving anti-PD-1 agents.^48–50 Exacerbation or reactivation of CMV and other herpesviruses has been observed with anti-PD-1 therapy in patients without HIV and is an important consideration when using these agents in PWH, especially those with CD4⁺ T-cell counts <100 cells/μL in whom risk of CMV disease is highest.^51,52

The participant who died from KSHV-associated B-cell lymphoproliferation had an elevated PBMC-associated KSHV viral load prior to initiation of pembrolizumab. This raised the possibility he may have had undiagnosed KSHV-associated MCD, an interleukin-6-related B-cell lymphoproliferative disorder associated with inflammatory symptoms, cytopenias, and an elevated peripheral blood KSHV viral load that can rapidly lead to death without treatment.⁵³ We could not rule out the possibility that pembrolizumab contributed to the worsening of this process. To mitigate potential risk to other participants, cohort 4 excluded participants with known active MCD as well as anemia or thrombocytopenia that could be suggestive of MCD. Importantly, KSHV-associated B-cell lymphoproliferation was not observed in the other 31 participants. Emergent KSHV-associated MCD was not described in any of the 15 participants with HIV-associated KS on AMC 095 or 35 participants in immune checkpoint blockade clinical trials in HIV-negative KS.⁴⁰ Longitudinal evaluation of the KSHV viral load in CITN-12 demonstrated no evidence of acute or long-term subclinical KSHV expansion, further supporting the safety of anti-PD1 therapy in KS. Pembrolizumab’s potential contribution to the development of MCD is also in contrast to the agent’s known activity in primary effusion lymphoma, an aggressive B-cell non-Hodgkin lymphoma also caused by KSHV.⁵⁴ This highlights the need for patients with symptoms of concurrent KSHV-associated diseases to be evaluated with appropriate diagnostic testing prior to receiving anti-PD-1 agents for KS.¹

Together with previous findings, our study has demonstrated the safety profile of pembrolizumab in KS and should dispel concerns that anti-PD-1 agents may have reduced activity among PWH, including those with low CD4⁺ T-cell counts. The high ORR supports a potential role for pembrolizumab for relapsed HIV-associated KS and as a first-line T-cell-sparing therapy in KS not responding to ART alone. KS is a severe and common tumor in areas of the world where KSHV and HIV prevalence are high, often affecting young people who may require KS therapy throughout their lifetime. Global efforts are required to establish randomized clinical trials against first-line standard-of-care therapies and implementation studies of anti-PD-1 agents in low-resource settings where the need for effective and durable KS therapies is highest.

Context Summary.

Key Objective

Is pembrolizumab safe and effective to treat HIV-associated Kaposi sarcoma (KS)?

Knowledge generated

This study of 32 participants demonstrated pembrolizumab is safe in HIV-associated KS. Potential exacerbations of opportunistic infections was an important safety finding. The overall response rate was 62% with KS responses noted among those with low CD4+ T-cell counts.

Relevance

Though monitoring for opportunistic infections is a caveat, these data are reassuring that immune responses against Kaposi sarcoma (KS) are observed not just in endemic KS, but also in HIV-associated KS, without detrimental effects on viral load or other complications.

Relevance section written by JCO Associate Editor Robert G. Maki, MD, PhD, FACP, FASCO