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Blood, 30 April 2009, Vol. 113, No. 18, pp. 4273-4280. Prepublished online as a Blood First Edition Paper on January 12, 2009; DOI 10.1182/blood-2008-09-181263.
IMMUNOBIOLOGY Cognate CD4 help is essential for the reactivation and expansion of CD8 memory T cells directed against the hematopoietic cell–specific dominant minor histocompatibility antigen, H601 Department of Biomedical Sciences, and 2 Graduate Program of Immunology, Seoul National University College of Medicine, Seoul; 3 Graduate School of Medicine, Korea University, Seoul; and 4 Division of Life and Pharmaceutical Sciences, Ewha Woman's University, Seoul, Korea
In contrast to previous notions of the help-independency of memory CD8 T cells during secondary expansion, here we show that CD4 help is indispensable for the re-expansion of once-helped memory CD8 T cells, using a hematopoietic cell–specific dominant minor histocompatibility (H) antigen, H60, as a model antigen. H60-specific memory CD8 T cells generated during a helped primary response vigorously expanded only when rechallenged under helped conditions. The help requirement for an optimal secondary response was confirmed by a reduction in peak size by CD4 depletion, and was reproduced after skin transplantation. Helpless conditions or noncognate separate help during the secondary response resulted in a significant reduction in the peak size and different response kinetics. Providing CD4 help again during a tertiary challenge restored robust memory expansion; however, the repeated deprivation of help further reduced clonal expansion. Adoptively transferred memory CD8 T cells did not proliferate in CD40L–/– hosts. In the CD40–/– hosts, marginal memory expansion was detected after priming with male H60 cells but was completely abolished by priming with peptide-loaded CD40–/– cells, suggesting the essential role of CD40 and CD40L in memory responses. These results provide insight into the control of minor H antigen-specific CD8 T-cell responses, to maximize the graft-versus-leukemia response.
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