Functional Evaluation and Genetic Evolution of Human T-cell Responses after Vaccination with a Conditionally Replication-Defective Cytomegalovirus Vaccine.

Background Cytomegalovirus (CMV) can cause congenital infection and is the leading cause of nongenetic newborn disabilities. V160, a conditionally replication-defective virus, is an investigational vaccine under evaluation for prevention of congenital CMV. The vaccine was well tolerated and induced both humoral and cellular immunity in CMV-seronegative trial participants [NCT10986010]. T-cell mediated immunity is important for immune control of CMV. Here we describe efforts to understand the quality attributes of the T-cell responses induced by vaccination. Methods Using multicolor flow cytometry, we analyzed vaccine-induced T-cells for memory phenotype, antigen specificity, cytokine profiles, and cytolytic potential. Moreover, antigen-specific T-cells were sorted from four participants and next generation sequencing was used to trace clonal lineage development during the course of vaccination using T-cell receptor β-chain (TCRβ) sequences as identifiers. Results The results demonstrated that vaccination elicited polyfunctional CD4 and CD8 T-cells to two dominant antigens, pp65 and IE1, with a predominantly effector phenotype. Analysis of TCR repertoires showed polyclonal expansion of pp65- and IE1-specific T-cells after vaccination. Conclusion V160 induced a genetically diverse and polyfunctional T-cell response and the data support further clinical development of V160 for prevention of CMV infection and congenital transmission.