Work

Early Post-Transplant Whole Tumor Cell-Based Vaccination Alters the Kinetics of T Cell Reconstitution

Year: 2012

Type: article

Abstract: Whole tumor cell-based vaccines administered in the early post-transplant (HSCT) setting are a promising approach to enhance graft-versus-leukemia responses. Our previous studies described the detection of increased CD8+ T cells with specificity for autologous chronic lymphocytic leukemia (CLL) cells in association with attainment of molecular remission within 6 months post-HSCT that developed following early-post transplant tumor vaccination (initiating at day 30-45). The series of vaccines were comprised of irradiated autologous tumor admixed with irradiated GM-CSF secreting bystander cells. It is unknown how this early post-transplant intervention shapes the reconstituting donor T cell repertoire. One approach to characterize this is through examining the kinetics of recovery of T cell receptor (TCR) beta-chain diversity using recently developed methodologies that apply deep sequencing techniques for the analysis of the highly variable complementarity-determining region 3 (CDR3) of the TCR. We therefore isolated naïve and memory T cells from the CD8 and CD4 compartments from 12 patients (6 with vaccine, 6 without) at time points informative for thymic-independent (early; 4 month post-transplant) and thymic-dependent (late; 1 year post-transplant) T cell immune recovery. The isolated cell subsets directly underwent PCR amplification of the CDR3 region to generate a template library that was then sequenced using the Illumina GA2 system. We obtained a median of 24,191 productive reads per sample (range 0-8,900,000). To evaluate the TCR diversity, we calculated the normalized probability distribution (‘entropy') of each T cell compartment. Overall, we observed that the 6 vaccinated subjects demonstrated a higher normalized entropy at day 120 (p = 0.008) and more unique CDR3 sequences (one-tailed t-test with unequal variance: p = 0.03) compared to non-vaccinated subjects. In particular, CD8+ memory and naïve cells exhibited greater TCR diversity at days 120 and 365 in vaccinated than in non-vaccinated individuals. These results suggest that early post-transplant vaccination exerts an active role in shaping T cell reconstitution. Ongoing analyses focus on the integration of TCR repertoire data with the assessment of minimal residue disease, immunophenotyping and TCR excision circle (TREC) analysis. The results gained within this study provide us with critical information as we formulate the next generation of post-transplant cancer vaccines.

Source: Transplantation and Cellular Therapy

DOI: 10.1016/j.bbmt.2011.12.064