Expression of HLA-B*35 Is Associated with an Increased Risk of CMV Viremia and Clinically Significant CMV Infection in Patients Receiving Ptcy-Based Hematopoietic Cell Transplantation

Introduction: Hematopoietic cell transplant (HCT) with post-transplant cyclophosphamide (PTCy) graft-versus-host disease (GvHD) prophylaxis is associated with an increased risk of cytomegalovirus (CMV) infections despite widespread use of prophylactic letermovir. T cell immune responses play a major role in control of viral infections such as CMV and may be affected by PTCy use via reduction of diversity in the TCR repertoire. A prior study (Hasan A, et al; Blood Adv 2022), demonstrated impaired control of CMV by CMVpp65 CTLs restricted by HLA-B*35 alleles. As this prior study included recipients of ex-vivo T cell depleted HCT, we hypothesized that expression of HLA-B*35 may be a risk factor for CMV infections after in vivo T cell depletion with PTCy-based HCT.

Methods: In this single-center retrospective study, we included consecutive adults at risk for CMV reactivation (recipient and/or donor seropositive) undergoing HCT with PTCy-based prophylaxis from February 2015 to February 2022. Patients were followed for one-year after HCT. CMV viremia and clinically significant CMV infection (CS-CMVi; CMV viremia or disease requiring CMV therapy) were assessed. Letermovir prophylaxis through D100 was used for CMV-seropositive recipients after 2017. Fine-Gray sub-distribution hazards models assessed risk factors associated with CS-CMVi and CMV viremia using disease relapse, repeat HCT, or death as competing risks. Tested covariates included age, sex, disease, HCT-CI, donor sex, donor match, letermovir use, CMV recipient and donor seropositivity, conditioning intensity, graft type, CD34⁺ cell dose, tocilizumab use, recipient HLA-B*35 positivity, and donor HLA-B*35 positivity. Cytokine release syndrome, neutrophil recovery, acute GVHD and chronic GVHD were included as time-varying covariates. This study was approved by the Dana-Farber Harvard Cancer Center (DF/HCC) Institutional Review Board.

Results: Of 211 patients meeting inclusion criteria, 59% were male and median age at HCT was 60 years (19.4 – 78.3). Acute myeloid leukemia was the most frequent primary disease (39%), followed by myelodysplastic syndrome or myeloproliferative neoplasm (29%), acute lymphoblastic leukemia (16%) and B-cell lymphomas (16%). HCT donor types included haploidentical (55%), HLA-mismatched unrelated (26%), and HLA-matched unrelated (19%). The majority of HCT recipients were CMV seropositive (78%). 127 patients (60%) received letermovir prophylaxis. At least one HLA-B*35 allele was carried by 38 (18%) patients. Transplant-related complications included CRS (47%), acute GVHD (42%), and chronic GVHD (27%). The one-year cumulative incidence of CS-CMVi was 29.9% (95% CI 23.8 - 36.1%). CMV end-organ disease occurred only in 3 patients (1.4%). On multivariable analysis, use of letermovir was associated with a decreased risk of CS-CMVi (HR 0.19 (95% CI 0.1 – 0.38), p<0.001). Recipient CMV seropositivity as well as recipient HLA-B*35 positivity were associated with an increased risk of CS-CMVi (HR 5.57 (95% CI 2.14 – 14.5), p<0.001 and HR 2.81 (95% CI 1.1 – 7.2), p=0.03, respectively) and CMV viremia (HR 4.87 (95% CI 2.35 – 10.1), p<0.001 and HR 2.28 (95% CI 1.15 – 4.55), p=0.02, respectively).

Discussion: In this study, HLA-B*35 recipient positivity was associated with an increased risk of CMV viremia and CS-CMVi suggesting a possible defect in CMV antigen presentation by HLA-B*35 bearing targets that may represent a novel tool to identify patients at risk of post-HCT CMV infection despite letermovir use. Future studies are needed to elucidate the mechanism and investigate how this may be used to identify and optimally manage patients at highest risk for CMV infections after HCT.