CMV Immunity Status in Older (>50 Years Old) Subjects after Non-Myeloablative or Reduced Intensity Regimen for Hematopoietic Cell Transplantation (HCT): A Comparison with a Younger Cohort after Ablative HCT.

Immunity declines with age as demonstrated by cell-mediated and humoral responses to alloantigens. The susceptibility of these elderly subjects to endogenous virus infection, such as human cytomegalovirus (HCMV) reactivation, is a particular concern during the process of hematopoietic stem cell transplantation (HCT) and immune reconstitution. In this report, the host contribution to stem cell engraftment and differentiation was evaluated by comparing the HCMV immune response in older subjects (> 50 y.o.) to a younger (< 50 y.o.) transplant population. This was a retrospective analysis of a subset of data collected prospectively and with IRB approval for characterization of the CMV immune response of allogeneic transplant patients. Within the dataset, two groups of patients were compared. Group 1 consisted of 10 patients >50 y.o. who had received reduced intensity or non-myeloablative conditioning regimen, and Group 2 consisted of 13 patients <50 y.o., most of whom had received a myeloablative regimen. Because 9 of 10 in Group 1 had had CMV reactivation, Group 2 was selected from the subset of younger patients with known post-transplant CMV infection. CMV infection was defined as either a positive CMV blood culture using shell vial assay or a positive CMV PCR on plasma. Subjects were assessed on days 40, 90, 120, 150, 180, and 360 post-HCT by CMV-specific tetramer-binding assay using CD8 cells, assays for intracellular INF-g response of CD4 and CD8 cells, and a T-cell receptor excision circle (TREC) assay. There were no significant differences observed in the CD4+/IFN-g+ cell responses to CMV antigen nor were the rates of activated CD4+/CD69+/IFN-g+ cells different between the groups. Group 1 was also characterized by a robust CD8+/IFN-g+ response to HLA-specific CMV peptides, and all subjects had ≥ 2cells/μl by day 150 post-HCT. The frequency of CMV tetramer positive cells (≥ 2cells/μl) was 50% in Group 1 by day 90 post-HCT and was not statistically different from Group 2. The T cell renewal in the thymus as measured by the TREC spanned over 0 -- 92 copies/μg of total cellular DNA in Group 1 and from 0 – 129 copies/μg in Group 2 during the first year post-HCT (n.s.). In conclusion, CMV immune reconstitution in older transplant subjects, who undergo a reduced intensity or non-myeloablative regimen, is robust and, in this small sampling, did not differ from that observed in a younger adult group.