A b s t r a c t s 23

INCIDENCE OF HLA-DP MISMATCHES ON MLR I RESPONSES IN UNRELATED HLA-A, B, DR, DQ, DW IDENTICAL PAIRS IN ALLOGENEIC BONE MARROW TRANSPLANTATION A Cesbron 1 , Ph Moreau 1-2, G Angelini 3 , N Milpied 2, JY Muller 1 , JL Harousseau 2, GB Ferrara 3,

JD Bignon I. 1- CRTS - HLA - BP 349 - 44011 NANTES Crdex 01 - France, 2- CHR - Hrmatologie Clinique - 44035 - NANTES Crdex - France 3- Istituto Nazionale per la Ricerca sul Cancro, GENOVA - Italy.

Allogenic bone marrow transplantation (BMT) remains a treatment of choice for many congenital and acquired desorders of the hematopoietic system. Its success relies on class I and class II HLA identity in the donor-recipient pairs serologic.ally (A, B, DR and DQ) and cellularly (Dw) studied - HLA-DP typing is not included in the usual compatibility studies before BMT and the role of DP products in primary mixed lymphocyte reaction (MLR) has not yet been clearly established.

RFLP typing of the potential unrelated donors, selected for their serological HLA-A, B, DR and DQ identity with our patients was prospectively performed (DRB, DQA and DQB probes, Taq I and Hind III enzymes). The Dw splits were identified by RFLP except for the donor-recipient pairs typed DR4 whose Dw subtypes were identified by PCR and oligotyping. Retrospectively, RFLP-DP typing (DP A and DP B probes, Taq I, Bgl II and Msp I enzymes) was carried out for 12 patients and their 25 selected DNA identical donors. In some cases, DP typing has been also performed by DNA amplification and hybridization with specific oligonucleotides according to G. Angelini (Human Immunology, 26 : 169 -1989). HLA-DP incompatibilities were then correlated with MLR I responses obtained in these 25 donor-recipient pairs (patient series) and in 33 donor pairs used as the control series. All these 58 pairs were HLA-A, -B, -DR, -DQ and -Dw identical.

This study demonstrates that : 1 - MLR I responses involving patients cells were always lower than those involving control cells (17.3 versus 31.1% in case of 2 DP-mismatches and 8 versus 21.6 % in case of 1 DP-mismatch). 2 - In case of no DP mismatch, no proliferative response was observed (cut off < 10 %). 3 - Two or one DP mismatches influence MLR I responses in 9 1 % and 77 % of the cases respectively with however a great scattering of values which could be explained by the dcgrcc t~l sequence homology between the DP mismatched alleles. 4 - "Fhc normal technical conditions of MLR I seem to not allow detection of mismat:.,es omer than Ihe well known HLA snecificities.

POTENTIAL UTILITY OF IRRADIATED DONOR ANTI-HOST CYTOTOXIC T- LYMPHOCYTES TO OVERCOME HOST RESISTANCE TO E N G R A F T M E N T OF HLA MISMATCHED T-CELL DEPLETED BONE MARROW. M.H.O. Porto, T.N. Small, A. Gilman, and N. Flomenberg. Memorial S loan-Ket ter ing Cancer Center, New York, N.Y. USA.

Studies of peripheral blood mononuclear cells obtained f rom patients undergoing marrow graft reject ion have pointed to the importance of residual host T-cells in the mechanism of graft fa i lure/re ject ion. Presumably these residual host T-cell populations are el iminated by donor T-cells contained in unseparated marrow grafts. We have performed a series of in vitro studies to investigate whether primed irradiated donor T-cells might safely be used therapeutical ly to prevent reject ion of T-cel l depleted marrow grafts. Radiosensit ivi ty studies of pr imed allocytotoxic T- lymphocytes demonstrated that cytolytic activity toward the specific allogeneic target cells was relatively well preserved when doses of i rradiat ion of up to 6000 rads were used. However, the alloproliferative capacity of pr imed T- lymphocytes to the same stimulator cells was decreased to less than 10% of the unir radia ted control with radiation doses above 3000 rads. To assess the potential s ignif icance of the residual 0-10% proliferation seen in short term assays, we investigated the long- term growth potential of these cells in l imiting dilution assays. These studies indicated that the irradiated primed cells are capable (at most) of only a few rounds of cell division. Thus there is a clear dissociation between capacity for DNA synthesis and CTL activity of previously primed T-cells af ter irradiation. These results suggest that irradiated pr imed CTL may not have long term G V H potential in vivo and that they might therefore be safely administered in the early post t ransplant period in at tempts to overcome residual host T-cells and facili tate engraf tment .