Potent Control of Acute Graft-Versus-Host Disease Lethality After Immunization With a Novel DNA Vaccine Targeted to B7-1/CD28 Costimulatory Signaling Pathway

A major challenge associated with allogeneic hematopoietic stem cell transplantation is effective prevention and/or attenuation of symptoms associated with acute graft-versus-host disease (aGVHD) that can result from a failure of either host and/ or donor CD4(+) CD25(+) regulatory T (Tr) and CD8(+) CD28(-) suppressor T (Ts) cells to dampen immunopathogenic responses mediated by alloreactive donor CD4(+) CD28(+) Th1 (Th1) and CD8(+) CD28(+) Tc1 (Tc1) cell-mediated inflammatory processes. Considering the crucial role of CD28/B7-1 costimulatory signal pathway in development, activation, differentiation, and function of these T subsets, we developed a targeted DNA vaccine encoding the Pseudomonas exotoxin-A and the B7-1 molecule that could act as both an antagonist to Th1-mediated and Tc1-mediated responses while concomitantly acting as an agonist stimulating Trmediated and Ts-mediated responses as a strategy for reducing aGVHD-associated lethality. A single intramuscular injection with this vaccine significantly increased Tr and Ts levels in a murine aGVHD model. In addition, immunized mice presented with significantly diminished Th1-cytokines interferon-g and interleukin-2 response and a moderately upregulated Th2-cytokine interleukin10 and Th3-cytokine transforming growth factor-b response. More importantly, vaccination significantly reduced aGVHD, measured by significantly extended mean survival times, decreased mean weight loss, recovery of peripheral leukocyte numbers, disease presentation associated with mild-moderate histopathologic changes, a balanced Th1-Th2-Th3-cytokine responses and functional Tr-mediated and Ts-mediated regulatory/suppressor mechanisms at levels more potent than observed in animals treated with cyclosporine A(+) methotrexate. Our data first provide the proofof- principal that B7-1-PE40KDEL targeted DNA vaccine represents a prophylactic approach for reducing alloreactive Th1mediated and Tc-mediated aGVHD lethality by CD28/B7-1 axis.