CD3/8 T-Cell Responses to CMV Reactivation in Patients Undergoing Haploidentical Transplants: A Retrospective Analysis

Introduction:

Cytomegalovirus (CMV) reactivation post allogeneic hematopoietic stem-cell transplant (HSCT) has been associated with reduced early relapse, particularly in acute myeloid leukemia (AML) patients treated with myeloablative (MA) conditioning. The underlying biologic mechanisms are unclear, but upregulation of cytotoxic lymphocytes in response to CMV reactivation has been suggested. However, overall survival (OS) in these patients does not improve, and non-relapse mortality (NRM) appears worse in some studies. Separately, inadequate lymphocyte recovery at day 100 has been associated with poorer OS and relapse incidence. The possible association between lymphocyte responses to CMV reactivation and outcomes has not been extensively studied in patients undergoing haploidentical (HI) HSCT. We examined the association between CMV reactivation and OS, NRM, relapse incidence and day+90 CD3/8 T-cell counts in this patient population.

Methods:

Retrospective data analysis was performed on 134 evaluable patients undergoing haploidentical transplants (all patients who were alive and had not relapsed at day 90 post-HSCT). The patients primarily underwent a T-replete, 2-Step HI MA or reduced intensity (RIC) HSCT at Thomas Jefferson University between 2006 and 2014. In the 2-Step approach, a large fixed dose of T cells (2 x 10⁸) is administered after conditioning (HSCT step 1), followed 2 days later by cyclophosphamide (CY) for T cell tolerization. Step 2 of the HSCT occurs with the infusion of a CD34 selected stem cell product, 1 day after the completion of CY. OS, NRM, and relapse incidence were compared between patients who were without versus with evidence of post HSCT CMV reactivation at day 90, which was defined by > 100 copies/ml by quantitative DNA PCR. Subgroup analysis to assess the relationship between CD 3/8 T-cell counts and CMV reactivation and their effect on OS using product limit survival estimates was performed on 118 patients with available CD3/8 T-cell counts at day +90. The median CD3/8 count for this group was 125 cells/μl; this level was used as the differentiator between high versus low CD 3/8 responses. Statistical analysis was performed with SAS.

Results:

CMV reactivation was detected in 62 of 134 (46.3%) patients. OS in CMV DNAemia+ vs. DNAemia- patients was 48% vs. 67% (Log Rank test, p=0.046). There were no significant differences in relapse and a non-significant increase in NRM based on CMV reactivation (Grays test, p=NS). CMV reactivation was strongly associated with increased CD 3/8 T-cell counts at day 90 post-HSCT (Wilcoxon test, p=0.0001). Using product limit survival estimates, we found that patients with no CMV reactivation and CD3/8 counts > 125 cells/μl at day 90 fared the best in terms of probability of OS at 2 years (84%), whereas those with CMV reactivation and CD3/8 counts < 125 cells/μl at day 90 fared the worst (50%). Patients with CD3/8 counts > 125 cells/μl reactivating CMV had OS rates of 59%. The difference in OS between these groups did not reach statistical significance, however. CD 3/8 T-cell counts greater than 125 cells/μl at day 90 were not associated with improved OS but were associated with a non-significant decrease in relapse incidence. These findings did not change after adjusting for acute graft-versus host disease, conditioning regimen (MA vs RIC) or disease subtype (AML versus non-AML).

Conclusion:

There was a significant association between CMV reactivation and quantitative CD3/8 T-cell responses in this population of patients primarily undergoing T-cell replete HI HSCT using the Jefferson 2-step approach. Despite this, CMV reactivation was associated with decreased OS in this population, perhaps related to the observed increase in NRM, although that did not reach statistical significance. There were no differences in relapse rates in patients with or without CMV reactivation. While not reaching statistical significance, there was a suggestion that higher CD3/8 T-cell counts at day +90 were partially protective against mortality in patients who developed a CMV DNAemia. Therefore, while T-cell responses to CMV may be helpful, other confounding factors such as coexisting GVHD, GVHD treatment with steroids, length of routine GVHD prophylaxis, and NK cell responses need to be studied in a multivariate setting to further explain the impact of CMV on OS.