Blockade of the CD40 and CD28/B7 Costimulatory Pathways in Peripheral Nerve Transplantation

Blockade of the CD40 costimulaatory pathway has been shown to permit regeneration through the peripheral nerve allograft. This strategy has been even more effective when combined with blockade of the CD28/B7 costimulatory pathway in models of organ transplantation. This study provided the first application of blockade of both the CD40 and CD28/B7 costimulatory pathways in the nerve allograft model using a brief course of treatment which was hypothesized to be sufficient for the temporary immunosuppressive requirements of the nerve allograft.

C57Bl/6 mice were recipients of Balb/c strain nerve allografts to reconstruct a 1-cm tibial nerve gap. Treatment consisted of MR1 (anti-CD40L monoclonal antibody) administered as 1 mg/kg, 3 doses on days 0, 2, 4 or as a single dose on day 0. CTLA4-lg (fusion protein blocking CD28/B7 pathway) was also tested as a single agent 0.5 mg/kg, or combined with MR1 using similar treatment protocols. Assessment consisted of walking track analysis for functional recovery, histomorphometric data for nerve regeneration, and ELISPOT assay for quantitative analysis of the host-immune response.

Histomorphometric data of total numbers of nerve fibers (TNNF) at the distal graft showed: allograft with no treatment 127 ± 180 TNNF; isograft with no treatment 650 ± 311 TNNF; 3 doses anti-CD40L monoclonal antibody generated 238 ± 368 TNNF; single dose of CTLA4-lg 29 ± 30 TNNF; 3 doses of CTLA4-lg combined with anti-CD-40L generated 589 ± 489; single dose of CTLA4-lg combined with anti-CD-40L generated 484 ± 445 TNNF. ELISPOT results demonstrated in vitro cytokin production by host cells in response to donor cells and were recorded as spots per millions cells (SPMC) positive for lFNg. In this study, 3 doses anti-CD40L monoclonal antibody generated 772 ± 19 SPMC; single dose of CTLA4-lg 1601 ± 166 SPMC; 3 doses of CTLA4-lg combined with anti-CD-40L generated 38 ± 12 SPMC; single dose of CTLA4-lg combined with anti-CD-40L generated 409 ± 155 SPMC.

Blockade of both the CD40 and CD28/B7 costimulatory pathways in the nerve allograft model using a brief course of treatment is sufficient for the temporary immunosuppressive requirements to allow axonal regeneration through the nerve allograft. The results demonstrate improved axonal regeneration with combined therapy over single antibody treatment and are consistent with the organ transplantation literature. Further studies examining longer and more frequent dosing regimens may demonstrate even greater axonal regeneration.