BALB/c TS1 transgenic RAG-deficient mice possess a univariate T-cell receptor (TCR) specific for the immunodominant epitope of influenza A virus PR8 hemagglutinin (HA) S1 determinant (aa 110-119) presented in the context of MHC class II IE^d. Naive donor CD4 T cells were isolated via flow sorting from unmanipulated TS1 mice. Memory populations were generated by isolating and stimulating these T cells in vitro for several days with HA S1 peptide and adoptively transferring them into BALB/c RAG-deficient mice for several months. Memory cell populations were then obtained by flow sorting. These subsets were then individually transplanted together with bone marrow from BALB/c RAG-deficient donors into lethally conditioned BALB/c transgenic mice (BALB/c HA104) expressing the HA S1 determinant throughout.¹³  Recipient mice were monitored, scored, and evaluated for clinical and histopathologic changes characteristic of GVHD. Professional illustration by Alice Y. Chen.