(A) Generation of transgenic antigen-specific T cells. Donor leukocytes are collected, enriched for Tm by CD45RA depletion or selection of virus-specific cells, transduced to express a transgenic TCR specific for a defined minor H antigen or LAA, purified, expanded, and infused into the recipient at the time of HCT or subsequently. The box depicts a schematic of transgenic TCR development (left to right): a T cell clone with a well-characterized high-affinity hematopoietically restricted minor H antigen– or LAA-specific TCR is identified and the α and β chains of the TCR are sequenced, and then cloned into a viral vector for transfer. (B) Primary in vitro stimulation of antigen-specific T cells. Donor leukocytes are stimulated with antigen-presenting cells (APCs) pulsed with peptides for one or multiple LAAs and/or minor H antigens to produce a T cell product with an expanded population of LAA- and/or minor H antigen–specific effector T cells for infusion into the recipient with or without additional enrichment. (C) In vivo expansion of antigen-specific T cells using vaccination. Donors are vaccinated against one or multiple LAAs and/or minor H antigens several months before HCT, using peptide- or cell-based vaccines, to allow formation of Tcm responses against the antigens. Antigen-specific Tcm are then transferred either with the PBSC graft at the time of HCT, or as DLI after HCT, with or without additional manipulation (e.g., further enrichment of Tcm or depletion of CD45RA⁺ cells) to reduce the risk of GVHD. Illustrated by Rachel Davidowitz.