Abstract
Background
Neutropenia is a serious complication following heart transplantation (OHT) however risk factors for its development and its association with outcomes is not well described. We sought to study the prevalence of neutropenia, risk factors associated with its development and its impact on infection, rejection and survival.
Methods
A retrospective single center analysis of adult OHT recipients from July 2004 to December 2017 was performed. Demographic, laboratory, medication, infection, rejection and survival data were collected for 1 year post-OHT. Baseline lab measurements were collected within the 24 hours before OHT. Neutropenia was defined as absolute neutrophil count ≤1000 cells/mm3. Cox proportional hazards models explored associations with time to first neutropenia. Associations between neutropenia, analyzed as a time-dependent covariate, with secondary outcomes of time to infection, rejection or death were also examined.
Results
Of 278 OHT recipients, 84 (30%) developed neutropenia at a median of 142 days (range 81-228) after transplant. Factors independently associated with increased risk of neutropenia included lower baseline WBC (HR 1.12; 95% CI 1.11 - 1.24), pre-OHT ventricular assist device (1.63; 1.00 - 2.66), high risk CMV serostatus [donor positive, recipient negative] (1.86; 1.19 - 2.88), and having a previous CMV infection (4.07; 3.92 - 13.7).
Conclusions
Neutropenia is a fairly common occurrence after adult OHT. CMV infection was associated with subsequent neutropenia, however no statistically significant differences in outcomes were found between neutropenic and non-neutropenic patients in this small study. It remains to be determined in future studies if medication changes in response to neutropenia would impact patient outcomes.
Keywords: neutropenia, heart transplant, CMV, infection
Introduction
Infection-related morbidity and mortality are common complications after orthotopic heart transplantation (OHT). 1 While neutropenia is a well-established risk factor for increased risk of infection in leukemic patients 2, risk factors for its development and its association with outcomes is not well described in OHT recipients. These patients receive multiple medications, including immunosuppressants and antimicrobial prophylaxis that are associated with the potential side effect of bone marrow toxicity. 3, 4 Certain opportunistic infections, particularly viral infections including Cytomegalovirus (CMV) reactivation, can also contribute to and be associated with low white blood cell (WBC) counts. 5 A better understanding of OHT recipients at increased risk for neutropenia could be beneficial to personalize immunosuppression and prophylactic antimicrobial medication type and enable one to predict and potentially mitigate myelotoxicity associated with these treatments. We also have little understanding of the consequences of neutropenia in this population. Therefore, we sought to study the incidence of neutropenia, risk factors associated with its development and the impact of neutropenia on infection, rejection and survival in the first year after OHT.
Methods
Study Population
All consecutive adult OHT recipients performed at Tufts Medical Center (Boston, MA) from January 2004-December 2017 were eligible for inclusion. Exclusion criteria included death within 72 hours, dual heart-kidney transplant, insufficient data in the medical record, and loss to follow-up within the first 3 months (Figure 1).
Figure 1. Flowchart of Cohort.
OHT: orthotopic heart transplant
Data collection
Demographic, laboratory, medication, infection, rejection and survival data were retrospectively collected from the medical record for 1 year following OHT.
Immunosuppression, antimicrobial prophylaxis and granulocyte colony-stimulating factor (G-CSF) data were collected during the index transplant hospital stay, and during each inpatient stay for the first year after OHT. Baseline laboratory measurements were collected within the 24 hours before OHT.
In addition, medication data was collected for the 4 weeks before and the 2 weeks after the first day of neutropenia. In those patients who did not become neutropenic, medication data was collected from the period spanning 4 weeks before until 2 weeks after the median day to first development of neutropenia to allow for a comparative 6 week window of time.
The Tufts Medical Center Institutional Review Board approved this study and the requirement for informed consent was waived.
Primary and Secondary Outcomes
Neutropenia was defined as an absolute neutrophil count (ANC) ≤ 1000 cells/mm3 based on our previous work and because our center initiates G-CSF treatment based on this threshold. 6 The primary outcome was time to first neutropenia (ANC ≤ 1000 cells/mm3) within 1 year of OHT. Secondary outcomes included all-cause mortality, time to first rejection and time to first infection within 1 year of OHT.
Immunosuppression protocols
Standard maintenance immunosuppression included a calcineurin inhibitor (tacrolimus), an antimetabolite (mycophenolate) and prednisone on a 6-month taper, if tolerated. Cytolytic anti-T cell antibody induction therapy was only used in select patients with impaired renal function, a positive cross-match or who were highly sensitized (class I calculated panel reactive antibodies > 50%) with either antithymocyte globulin, muromonab-CD3 or basiliximab. If the recipient was highly sensitized, rituximab was also administered. Cellular rejection episodes were uniformly treated with 3 g of IV methylprednisolone and, if refractory, then with anti-T cell antibody treatment. Antibody-mediated rejection episodes were treated with 3 g intravenous (IV) methylprednisolone, plasmapheresis, and, in eligible patients, rituximab and/or intravenous immunoglobulin.
Rejection Definition and Treatment
Rejection was defined as the composite of a first episode of biopsy-proven cellular rejection requiring admission for IV corticosteroids or parenteral anti-T cell antibody therapies, antibody-mediated rejection requiring admission for IV corticosteroids, plasmapheresis, or other parenteral therapies (rituximab and/or intravenous immunoglobulin), or any rejection episode causing hemodynamic compromise, graft loss, re-transplantation, or death. 7, 8
Infection Definitions
We used a composite infectious outcome which included CMV infection, bloodstream infection (BSI), invasive fungal infection (IFI) and other opportunistic infections (e.g. Nocardia). All infections were adjudicated by a panel of three Transplant Infectious Disease physicians who were blinded to the patient’s neutropenia status.
Cytomegalovirus Infection and Disease
CMV disease was defined according to the criteria of the CMV consensus conference definitions which have been used in other studies. 5, 9, 10
CMV infection is evidence of CMV replication regardless of symptoms; “defined as virus isolation or detection of viral proteins (antigens) or nucleic acid in any body fluid or tissue specimen”.
CMV disease is evidence of CMV infection with attributable symptoms. “CMV disease can be further categorized as a viral syndrome (i.e. fever, malaise, leukopenia, and/or thrombocytopenia), or as tissue invasive (“end organ”) disease.”
Blood Stream Infection
BSI was defined as positive blood cultures in accordance with previous definitions 11. Bacteremia caused by common skin contaminants was considered significant if the same organism was isolated from two blood cultures in the presence of clinical signs of infection and/or an intravascular device. 12
Invasive Fungal Infection
IFI was defined as identification of fungal species by culture or histological examination from a normally sterile site as per the 2008 EORTC/MSGERC criteria. 13, 14 Solitary sputum, urine or non-sterile site cultures were not considered an IFI.
CMV and Antimicrobial Prophylaxis
Primary CMV prophylaxis was routinely used except in those who were donor and recipient seronegative. Those at intermediate risk (CMV R+) received 3 months of oral valganciclovir 900 mg once daily, with doses adjusted for renal impairment. In those at highest risk (CMV D+/R−), the duration of prophylaxis ,was extended from 3 to 6 months in 2008. In addition, 7 doses of CMV immune globulin was routinely used in the highest risk group for prophylaxis from 2004 until 2015. Routine CMV viral load monitoring after primary prophylaxis did not start until 2017 10.
Our standard Pneumocystis jirovecii prophylaxis was trimethoprim-sulfamethoxazole (TMP-SMX) for 12 months; atovaquone or dapsone were substituted in cases of allergy or perceived toxicity.
Statistical Analysis
Non-neutropenic and neutropenic patients were described using percentages, means with standard deviations and medians with interquartile ranges
Cox proportional hazards models explored unadjusted and adjusted associations of patient characteristics with the primary outcome of time to first neutropenia. Covariates with a p value of < 0.05 on univariate analysis were included in the multivariable analysis using best subsets selection and further informed using clinical judgement of known risk factors for neutropenia. Time-dependent covariates included rejection and infection. Censoring occurred for loss-to-follow-up, death or at one year post-transplant. Schoenfeld residuals were tested to verify that proportional hazards assumptions were not violated in the final multivariable model. 15
Associations between neutropenia, analyzed as a time-dependent covariate, with the secondary outcomes of time to infection, rejection, or death were also examined individually.
Sensitivity analyses were performed using a lower neutropenia threshold of ANC <500 cells/mm3 as the outcome definition. The distribution of valganciclovir exposure by high risk CMV serostatus was examined using Chi-square testing. To explore whether the association between CMV serostatus and neutropenia was independent of valganciclovir exposure, a sensitivity analysis was performed which forced valganciclovir into the multivariable model. Further sensitivity analyses explored the impact of myelotoxic medications, mycophenolate and TMP-SMX, on the multivariable model. The medication variables were included using two different measurements of medication exposure: 1) at time of index hospital discharge and 2) any time during the 4 weeks before and 2 weeks after the median time to development of neutropenia.
Statistical analyses were completed using SAS 9.4 (Cary, NC). All p-values were two-sided and p <0.05 was considered statistically significant.
Results
Demographics
After applying exclusion criteria, our analysis cohort included 278 OHT recipients who were transplanted from July 2004 to December 2017 (Figure 1). The majority were white (82%) males (72%) with a mean age of 53 at time of transplant. The most common indication for transplant was non-ischemic cardiomyopathy (64%) and nearly two thirds had a durable ventricular assist device (VAD) pre-OHT (Table 1). Nearly one third of the cohort was in the highest risk CMV group (donor seropositive and recipient seronegative).
Table 1.
Characteristics of heart transplant recipients with and without neutropenia
| Total, N=278 | Neutropenia, N=84 | No Neutropenia, N=194 | |
|---|---|---|---|
| Pre-transplant | |||
| Male, N (%) | 201 (72.3) | 59 (70.2) | 142 (73.2) |
| Hispanic | 27 (9.7) | 7 (8.3) | 20 (10.3) |
| White | 228 (82) | 73 (86.9) | 155 (79.9) |
| Black | 18 (6.5) | 3 (3.6) | 15 (7.7) |
| Asian | 5 (1.8) | 1 (1.2) | 4 (2.1) |
| Age, years , mean (SD) | 52.6 (12.0) | 53.5 (11.8) | 52.3 (12.0) |
| BMI, kg/m2 | 27.7 (5.5) | 28.4 (6.1) | 27.4 (5.2) |
| †Baseline WBC, cells /mm3 | 8.1 (2.9) | 7.5 (2.3) | 8.3 (3.1) |
| Baseline ANC, cells/mm3 | 5.5 (2.6) | 5.1 (1.9) | 5.7 ‡(2.9) |
| Baseline Creatinine, mg/dL | 1.2 (0.4) | 1.3 (0.5) | 1.2 (0.4) |
| §Baseline GFR <= 60, mL/min/1.73 m2 | 111 (39.9) | 84 (50) | 69 (35.6) |
| CKD, N (%) | 83 (29.9) | 28 (33.3) | 55 (28.4) |
| Diabetes | 95 (34.2) | 28 (33.3) | 67 (34.5) |
| Solid Tumor | 14 (5) | 2 (2.4) | 12 (6.2) |
| Heme Malignancy | 18 (6.5) | 2 (2.4) | 16 (8.2) |
| Autoimmune Disease | 10 (3.6) | 3 (3.6) | 7 (3.6) |
| Ischemic Cardiomyopathy | 101 (36.3) | 32 (38.1) | 69 (35.6) |
| Non-Ischemic Cardiomyopathy | 179 (64.4) | 52 (61.9) | 127 (65.5) |
| Giant Cell myocarditis | 5 (1.8) | 3 (3.6) | 2 (1) |
| Durable VAD | 181 (65.1) | 62 (73.8) | 119 (61.3) |
| IABP | 14 (5) | 3 (3.6) | 11 (5.7) |
| Extracorporeal Surgically Implanted MCS | 2 (0.7) | 1 (1.2) | 1 (0.5) |
| ECMO | 1 (0.4) | 0 (0) | 1 (0.01) |
| Post-Transplant | |||
| CMV serostatus | |||
| CMV D+R− | 85 (30.6) | 37 (44) | 48 (24.7) |
| CMV D+R+ | 63 (22.7) | 19 (22.6) | 44 (22.7) |
| CMV D−R+ | 56 (20.1) | 13 (15.5) | 43 (22.2) |
| CMV D−R− | 74 (26.6) | 15 (17.9) | 59 (30.4) |
| Hemodialysis | 30 (10.8) | 12 (14.3) | 18 (9.3) |
| Hospital length of stay, days, median (25%-75%) | 14 (11- 18) | 14 (11.5 - 19) | 14 (11- 18) |
| Outcomes Post-Transplant; Pre and Post Neutropenia | |||
| Infection | 74 (26.6) | 34 (40.5) | 40 (20.1) |
| Rejection | 65 (23.4) | 21 (25) | 44 (22.7) |
| Death | 13 (4.7) | 4 (4.8) | 9 (4.6) |
| Medications at discharge | |||
| Mycophenolate | 265 (95.3) | 81 (96.4) | 184 (94.8) |
| Sirolimus | 11 (4) | 4 (4.8) | 7 (3.6) |
| Cyclosporine | 56 (20.1) | 7 (8.3) | 49 (25.3) |
| Tacrolimus | 217 (78.1) | 72 (85.7) | 145 (74.7) |
| TMP-SMX | 235 (84.5) | 70 (83.3) | 165 (85.1) |
| Ganciclovir or Valganciclovir | 202 (72.7) | 68 (81) | 134 (69.1) |
| ¶ Medications During Neutropenia Period | |||
| Tacrolimus | 216 (79.1) | 74 (88.1) | 142 (75.1) |
| Sirolimus | 7 (2.5) | 3 (3.6) | 4 (2.1) |
| Cyclosporine | 50 (18) | 7 (8.3) | 43 (22.2) |
| Mycophenolate | 251 (91.9) | 77 (91.7) | 174 (92.1) |
| Azathioprine | 7 (2.5) | 3 (3.6) | 4 (2.1) |
| Anti-T-cell agent | 38 (14) | 18 (21.7) | 20 (10.6) |
| TMP-SMX | 220 (80.6) | 62 (73.8) | 158 (83.6) |
| Dapsone | 19 (6.8) | 10 (11.9) | 9 (4.6) |
| Ganciclovir or Valganciclovir | 144 (52.7) | 57 (67.9) | 87 (46) |
| G-CSF | 51 (18.3) | 47 (56) | 4 (2.1) |
Abbreviations: BMI: body mass index, WBC: white blood cell, ANC: absolute neutrophil count, GFR: glomerular filtration rate, CKD: chronic kidney disease, VAD: ventricular assist device, IABP: intra-aortic balloon pump, MCS: mechanical cardiac support, ECMO: extracorporeal membrane oxygenation, CMV: Cytomegalovirus, D: donor, R: recipient, TMP-SMX: trimethoprim sulfamethoxazole, G-CSF: granulocyte colony stimulating factor.
baseline was within 24 hours before transplant
missing N=38
CKD-EPI equation [30]
defined as 4 weeks before and 2 weeks after date of onset of ANC ≤ 1000 cells/mm3
Neutropenia
Of 278 OHT recipients, 84 (30%) developed neutropenia within a median of 142 days (interquartile range [IQR]: 1-228) after transplant. More than half (56%) of those with neutropenia were treated with G-CSF. The mean ANC among those who became neutropenic was 800 cells/mm3 (SD 200 cells/mm3).
Those who became neutropenic had lower WBC and worse renal function at pre-transplant baseline. More patients who developed neutropenia had durable VADs pre-OHT and were in the highest risk CMV serostatus group (Table 1).
At time of discharge from the hospital after transplant, patients who became neutropenic were more likely to be on tacrolimus and ganciclovir/valganciclovir, and less likely to be on cyclosporine. During the 4 weeks before and the 2 weeks after the first day of neutropenia, patients who developed neutropenia were more likely to be on tacrolimus, ganciclovir/valganciclovir, dapsone and G-CSF, and less likely to be on cyclosporine compared to those who were not neutropenic during the same snapshot of time around a median of 142 days post-OHT.
When the cohort was divided into tertiles, 22% (20/93) of recipients developed neutropenia between 2004-2009, 33% (27/81) developed neutropenia between 2010-2014, and 36% (37/104) developed neutropenia between 2015-2017; however, the global trend was not statistically significant (P=0.08).
Risk factors for Neutropenia
Factors associated with increased risk of neutropenia are shown in Table 2. On univariate analysis, pre-OHT factors associated with neutropenia included baseline eGFR ≤60 mL/min/1.73m2, lower baseline WBC, and having a durable VAD. Post-OHT factors associated with neutropenia included longer length of index transplant hospital stay, high risk CMV serostatus (D+/R−), being prescribed valganciclovir at time of hospital discharge, and previous CMV infection, which was treated as a time-dependent covariate.
Table 2.
Associations of Risk factors with Outcome of Neutropenia
| Unadjusted Hazard Ratio (HR) |
95% Confidence Interval (CI) |
Adjusted HR | 95% CI | ||
|---|---|---|---|---|---|
| Lower Baseline WBC per unit/mm3 | 1.10 | 1.01-1.21 | 1.12 | 1.11-1.24 | |
| Pre-Transplant Left Ventricular Assist Device | 1.63 | 1.01-2.66 | 1.63 | 1.00-2.66 | |
| Baseline eGFR ≤ 60 mL/min/1.73m2 | 1.56 | 1.02-2.39 | Not in adjusted model | ||
| High Risk CMV Serostatus (D+/R−) | 1.87 | 1.21-2.88 | 1.86 | 1.19-2.88 | |
| Length of Transplant Hospital Stay (per week) | 1.05 | 1.01-1.10 | Not in adjusted model | ||
| Valganciclovir at Time of Hospital Discharge | 2.14 | 1.35-3.38 | Not in adjusted model | ||
| Previous CMV infection – time dependent | 8.40 | 4.52-15.6 | 4.07 | 3.92-13.7 | |
Abbreviations: WBC: white blood cell; eGFR: estimated glomerular filtration rate; CMV: cytomegalovirus, D: donor, R: recipient,
In the adjusted model, previous CMV infection had a four-fold increased association for the development of neutropenia. High risk CMV serostatus, lower baseline WBC and having a pre-OHT VAD were also independently associated with developing neutropenia. The multivariable model met proportional hazards assumptions.
Though the frequency of neutropenia increased by year of transplantation, with more present during the latter years, adjusting for year of transplant did not significantly change the adjusted hazard ratio results (data not shown).
Sensitivity Analyses
When the neutropenia outcome was defined as <500 cells/ mm3, this lower threshold reduced the number of outcomes from 84 to 17. In univariate analysis, none of the risk factors from the multivariable model (previous CMV infection, high risk CMV serostatus, lower baseline WBC, having a pre-OHT VAD) were statistically significant (data not shown).
To ensure high risk CMV serostatus was not simply a surrogate marker for exposure to valganciclovir, we verified that 119 patients, or 43% of the entire cohort, were non-high risk CMV serostatus and were on valganciclovir at time of hospital discharge (data not shown). When valganciclovir treatment variables were forced into the multivariable model, they were not statistically significant, however high risk CMV serostatus and previous CMV infection both continued to be significantly associated with neutropenia (see Supplementary Table 1).
To further explore other known myelotoxic medications, mycophenolate and TMP-SMX exposure variables were forced into the multivariable models, however they were not statistically significant (see Supplementary Table 2). When other combinations of TMP-SMX, mycophenolate and valganciclovir exposure variables were included in the multivariable model, none of the medication variables were statistically significant (data not shown).
Neutropenia and Secondary Outcomes
Within 1 year of OHT, 27% (N=74) of patients developed infection at a mean of 183 (SD 94) days after OHT, 23% (N=65) developed rejection at a median of 85 (IQR: 8 - 16) days post-OHT and 5% (N=13) died at a median of 80 (IQR: 41 - 249) days post-OHT.
We did not find statistically significant associations between neutropenia and the secondary outcomes of infection [hazard ratio (HR) 0.98; 95% confidence interval (CI): 0.52 -1.84], rejection (HR 1.89; 95% CI: 0.91 - 3.96), or death (HR 4.00; 95% CI: 0.98 - 16.3); however there were few events occurring after neutropenia and before 1 year post-OHT. There were only 9 patients with infection, 5 patients with rejection and 4 patients who died.
Infections
Infections in neutropenic and non-neutropenic patients are shown in Table 3. Other infections included Nocardia, atypical mycobacteria and EBV-associated post-transplant lymphoproliferative disease.
Table 3.
Infections in Heart Transplant Recipients within the First Year
| Infection Type, N, (%) |
Neutropenia (N=34) | No Neutropenia (N=40) | Total (N=74) |
|---|---|---|---|
| CMV | 25 (74) | 20 (50) | 45 (61) |
| BSI | 3 (12.5) | 10 (25) | 13 (18) |
| IFI | 3 (12.5) | 8 (20) | 11 (15) |
| Other | 3 (12.5) | 3 (7.5) | 5 (7) |
Abbreviations: CMV: cytomegalovirus, BSI: bloodstream infection, IFI: invasive fungal infection.
Most infections were CMV disease whether they occurred before (14/22, 64%), concurrent with (3/3, 100%) or after (8/9, 89%) neutropenia, or in the absence of neutropenia (20/40, 50%). Those with high risk CMV serostatus had the highest frequency of CMV infections in contrast to BSI and IFI which were more frequent in those without high risk CMV serostatus. The majority of CMV infections were gastrointestinal disease (64%), followed by CMV syndrome (27%) with the remaining being asymptomatic CMV DNAemia (9%).
The frequency of infections increased over time, particularly after 2015, and this was a statistically significant trend (p=0.01). When the cohort was divided into tertiles, 22% (20/93) of recipients developed infection between 2004-2009, 20% (16/81) developed infection between 2010-2014, and 37% (38/104) developed infection between 2015-2017.
Discussion
This retrospective cohort study describes neutropenia with an ANC ≤1000 cells/mm3 as a common occurrence in the first year post-OHT with an incidence of 30% at a median time close to 5 months after transplant. This frequency of neutropenia is similar to a kidney transplant cohort 16 and in between the incidence reported by Mavrakanas et al. in kidney transplants (20%) and liver transplants (38%). 17 The timing of post-OHT neutropenia is similar to other recently published reports of mild neutropenia after lung transplantation 18 and neutropenia occurring after pediatric OHT. 19
We found high risk CMV serostatus (D+/R−), previous CMV disease, lower pre-transplant WBC and pre-transplant VADs were independently associated with the development of neutropenia within the first year post-OHT. While there have been other studies examining neutropenia in intra-abdominal organ transplants 17, lung transplants 18, and pediatric OHTs 19, this is one of the first studies, to our knowledge, to examine neutropenia in adult OHT recipients.
High-risk CMV serostatus 17, 18, 20 and CMV disease 6 have previously been shown to be associated with neutropenia post-solid organ transplantation (SOT). High risk CMV serostatus, by definition, is associated with an increased risk for CMV infection 10, yet both high risk CMV serostatus and previous CMV infection each independently increase the hazard for neutropenia after OHT. These two factors could be proxies for the amount of exposure to prophylaxis and treatment with CMV medications, ganciclovir and valganciclovir, which are known to have bone marrow suppressive effects. 3, 4, 21, 22 Other studies have found relationships between valganciclovir use and neutropenia post-transplant. 17, 23 Our study found exposure to CMV treatment at time of hospital discharge was associated with neutropenia on univariate analysis, however this association disappeared after adjusting for high risk CMV serostatus and previous CMV infection. Our findings suggest that high risk CMV serostatus and previous CMV infection confer risk for neutropenia beyond that attributed to valganciclovir exposure alone. We only collected medication data at certain cross-sectional time points and did not measure the cumulative exposure to ganciclvoir and valganciclovir. It is possible that cumulative exposure to these anti-CMV medications would be the strongest risk factor for developing neutropenia after OHT. However, in addition to being a proxy for exposure to CMV treatment medications, CMV infection itself could have other direct or indirect effects on the bone marrow to further explain its independent association with neutropenia. 5
The independent association of a pre-transplant VAD with subsequent neutropenia was an unexpected finding. The biomaterials and sheer stress to the circulatory system of sustained VAD exposure can affect the inflammatory phenotype when compared to heart failure patients not on mechanical support. 24 Prolonged LVAD exposure has been associated with impaired cell-mediated immunity due to downregulation of normal proliferative responses. Animal models have suggested that artificial devices might even induce permanent changes to the immune system. 25 One potential hypothesis to explain the association between VADs and neutropenia is that VAD-induced chronic inflammation primes the OHT recipient’s bone marrow to be more susceptible to myelotoxic viral and/or medication effects in the post-OHT setting leading to more frequent neutropenia.
Our sample size was too small to explore the associations between neutropenia and the outcomes of infection, rejection and all-cause mortality. The data in the literature supporting these associations have been inconsistent. We previously found increased risk of BSIs amongst liver transplant recipients with neutropenia. 6 In a kidney transplant cohort, neutropenia was associated with bacterial and CMV disease, and this relationship was associated with degree of neutropenia but not with its duration. 16 In a lung transplant cohort, neutropenia was a risk factor for gram positive and gram negative infections but not CMV infection. Other studies have not found an increased risk of infection amongst solid organ transplant (SOT) recipients with neutropenia. 3, 4, 17, 19 Similarly, some studies have found increased rates of rejection amongst SOT recipients 23 or kidney transplant recipients 17, 23, but this was not corroborated by other studies. 6, 16, 18, 19 For all-cause mortality, an increased risk was found in most studies 6, 17, 18, 26, but others found no association between neutropenia and mortality. 16, 23
The etiology of neutropenia in the post-SOT setting is likely multifactorial from a combination of immunosuppressive medications, antimicrobial prophylactic medications, especially anti-virals such as valganciclovir, and infection, including CMV disease. 5, 21 While our study did not find independent associations between any medication exposure and neutropenia, the characterization of medication exposure lacked detail. Mycophenolate mofetil is one of the potential causes of bone marrow suppression, however reducing immunosuppression can lead to an increased risk of graft rejection. 16, 27 Valganciclovir use, particularly in combination with mycophenolate, is also associated with leukopenia and neutropenia when used for universal CMV prophylaxis. 3, 21 In a recent study in liver transplant recipients, a pre-emptive treatment approach to CMV infection was compared to universal CMV prophylaxis in a high-risk CMV serostatus cohort. 28 Neutropenia did not differ between treatment arms and though a lower incidence of CMV was found in the pre-emptive group, the absolute difference was modest and these findings may not be applicable to non-liver transplant patients. The pre-emptive approach to CMV treatment is also very resource and labor intensive and may not be practical in many settings. An alternative to the pre-emptive approach to preventing CMV disease would be to using universal prophylaxis with the newer anti-CMV agent, letermovir, which is not myelotoxic. 29 In a randomized, placebo-controlled trial in hematopoetic stem cell transplant recipients, letermovir prophylaxis resulted in a significantly lower risk of clinically significant CMV infection and was well tolerated with similar myelotoxicity to placebo. 30
Limitations
Our study has several limitations. It was a single-center retrospective study in OHT recipients over a 13 year time period during which immunosuppression and antimicrobial regimens changed and surgical and medical management of pre and post-OHT patients also evolved. We included year of transplant in our final model to attempt to account for these changes, but this did not significantly change the models. Since it was retrospective, our study may not have captured all confounders for neutropenia. Our findings may also not be applicable to other types of SOTs. Though we used time-dependent measurements of the primary outcome of neutropenia, we did not collect daily medication data nor medication dosing to calculate cumulative exposure to medications, such as anti-metabolites or valganciclovir. Because our study was retrospective and focused on objective definitions of infections, bacterial infections such as pneumonia, cellulitis or urinary tract infection were not included. This narrow infection definition could help explain why an association between neutropenia and infection was not observed. Our findings of high risk CMV serostatus and previous CMV infection as independent risk factors for neutropenia could be proxies for cumulative exposure to ganciclovir and valganciclovir, however our data also show that these CMV-related factors are associated with neutropenia independent from at least simple measures of antiviral exposure. Unlike multiple previous studies 6, 16-18, 26, we did not find relationships between neutropenia and the time-dependent secondary outcomes of infection, rejection and mortality, however our numbers of these events were small in our one year of post-transplant follow-up.
In conclusion, neutropenia is a common occurrence after adult OHT occurring in nearly one third of patients within the first year. High risk CMV serostatus and CMV infection were independently associated with subsequent neutropenia, however adverse outcomes (infection, rejection, death) were similar in neutropenic and non-neutropenic patients in this small study. If high risk CMV serostatus and CMV infection are assumed to be partial surrogate measures of exposure to myelotoxic anti-CMV medications, such as valganciclovir, the use of bone marrow sparing letermovir as an alternative for CMV prophylaxis could prevent the development of so much neutropenia post-OHT. Further studies are needed to clarify if medication changes to prevent neutropenia could impact patient outcomes.
Supplementary Material
Acknowledgements
This study was supported by an unrestricted grant by Merck and NIH CTSA award: UL1TR002544, and also, in part, by generous donations to the Tupper Research Fund at Tufts Medical Center.
We would also like to acknowledge the following individuals for help with data collection: Julia Parker, Haley Hauck. We would also like to thank Janis Breeze, MPH for help with statistical interpretation.
Financial Disclosure Statement
JC has received grant support from Merck.
AV has received grant support from the American Heart Association, the National Institutes of Health and has participated in clinical trials with Corvia, Boehringer-Ingelheim, and CareDx.
DRS has been a consultant for Merck, Takeda, IQVIA, Visterra, and ReViral and has received grant support form Merck, Summit and Takeda.
Footnotes
The other authors do not have any financial conflicts to disclose.
Reference List
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