SYNERGY OF 15-DEOXYSPERGUALIN WITH ANTICD3 IMMUNOTOXIN IN TOLERANCE INDUCTION IN RHESUS MONKEYS

Abstract

60 Introduction. T cell depletion therapy with antiCD3 immunotoxin (αCD3IT) promotes long-term (≥1 yr) allograft survival without chronic immunosuppressive drugs in rhesus monkeys. In a preliminary study, administration of adjunctive peritransplant immunosuppression with 15-Deoxyspergualin (DSG) showed promise in enhancing LTS. Here, in an expanded series of transplants induced with CD3IT on day 0, with and without DSG, we examined the incidence of LTS and development of specific antidonor antibody. Methods. Normal 3 kg rhesus monkeys (n=46) received an MHC mismatched KTx with αCD3IT treatment administered on day 0-2 at a total dose of 133-150 ug/ml. Recipients were divided into 2 groups: those that received DSG and those that did not. DSG was given i.v. at 2.5 mg/kg on days 0-14. Censored from the graft survival analysis were non-rejection failures with creatinine<1.2 and without biopsy proven rejection (n=8, eg., 2 bloat, 1 hypercalcemia, 1 aspiration, 1 anesthesia, 3 wasting). In 30 recipients we examined production of antidonor specific serum IgM and IgG during the 1st 2 months by flow cytometry crossmatch (FCM) on gated B (CD20+) and T(CD3+) cells. Donor specific antibody was assigned positive when the B cell median channel shift was 2SD above the negative control and showed allospecificity. Development of T cell pos/ B cell neg FCM was presumed to be an anti-idiotypic response to αCD3IT. Results. Actual 1-year survival (LTS) was 64% in the DSG treated group (n=11) and 15% in the DSG non-treated group (n=27) (p=0.005). LTS associated with complete inhibition of the IgM antidonor (B cellpos FCM) response in the 1st two months: In LTS there were 0/9 IgM antidonor responders, but 8/21 in the rejectors (p=0.03). This significant association was not observed with IgG, likely due to the brevity (2 months) of antibody follow up. In contrast, the nonspecific, anti-T cell response (TposBneg FCM, putative CD3 anti-idiotype) was not inhibited and showed no association with immunologic rejection or LTS. Thus, inhibition of the development of IgM antidonor B cellpos FCM appeared to be both complete and specific in LTS recipients. This effect was related to DSG treatment as only 14% of the antidonor responders were in the DSG treated group. DSG failed to inhibit the putative anti-CD3 idiotype response (TposBneg FCM). Conclusions. This study suggests a beneficial effect of peritransplant DSG in promoting LTS in monkey recipients with αCD3IT. The DSG effect is reflected by a complete, apparently restricted suppression of antidonor antibody in the first 2 months, suggesting the action of DSG is focused on antigen presentation of donor MHC during T cell repopulation. (This work was supported in part by the Novartis Pharmaceuticals Corp., East Hanover, NJ)