Amal Bishara

Alloreactivity of umbilical cord blood mononuclear cells: specific hyporesponse to noninherited maternal antigens

Earlier studies noted that patients who underwent cord blood (CB) transplantation had a lower incidence of graft-versus-host disease (GVHD) than those who underwent bone marrow transplantation (BMT). The premise that the immune reactivity of CB mononuclear cells (CB-MNC) to HLA mismatched combinations and to noninherited maternal antigens (NIMA) may be one of the factors involved in this phenomenon is still debatable. In this study we have attempted to evaluate the alloresponse and alloreactivity induced by CB-MNC by means of the standard mixed lymphocyte reaction test (SMLR) and the more sensitive, modified mixed lymphocyte reaction test (MMLR). Both techniques were used to test CB-MNC (n = 28) against HLA class II mismatched MNC from mothers (n = 26), fathers (n = 12), and unrelated individuals (n = 60) who served as controls. Alloresponse capabilities and stimulation capacities of CB-MNC in the SMLR were similar to those of control MNC: relative response (RR) = 73 vs. 65 and 58 vs. 65, respectively. Similar results were obtained in the MMLR. CB-MNC responded weakly to the maternal MNC in comparison with control MNC (RR = 47 vs. 73 [p = 0.0099]), while a stronger response was noted to the paternal than the maternal MNC (RR = 72 vs. 47 [p = 0.045]). Our results demonstrate that CB-MNC both respond to and induce alloresponse in HLA mismatched combinations. Moreover, the hyporesponse of CB-MNC to maternal cells that we observed suggests a form of tolerance to NIMA, which is probably due to the fetuss exposure to these antigens in its intrauterine life.

Prediction by a modified mixed leukocyte reaction assay of graft-versus-host disease and graft rejection after allogeneic bone marrow transplantation

In this report we describe a modified, sensitive MLR test that appears to detect fine antigenic disparities between HLA-identical siblings confirmed as such by serology and the standard MLR test. In a group of 40 consecutive allogeneic bone marrow transplants, reactivity detected by the modified MLR test correlated with the development of rejection of matched marrow grafts and onset of acute graft vs. host disease (aGVHD). Thus, 13/15 positively reacting patient/donor pairs developed one of these complications (P < 0.001), while only 2/25 developed aGVHD in the negatively reacting group. This test may be useful for selecting the most compatible donor when several potential donors are available.

Is presensitization relevant to liver transplantation outcome

The impact of anti-HLA antibodies and crossmatch (CM) on liver transplantation (LT) outcome is still controversial. In this retrospective study we analyzed LT outcome according to pretransplant pre-formed anti-HLA antibodies and CM status. Serum anti-HLA antibodies were screened by ELISA assay, utilizing One Lambda antigen tray-mixed (LAT-M). CMs were performed by the complement dependent cytotoxicity test using Dithiotreitol treated sera. Anti-HLA antibodies were studied in 80 recipients; 56/80 had positive LAT-M tests (PLAT-M), whereas the remaining 24 recipients tested negative for both classes I and II (NLAT-M). Rejection episodes were more frequent in PLAT-M compared with NLAT-M group in post-LT intervals of <1 week (p = 0.05), 1 week-3 months (p = 0.035), and 3-12 months (p = 0.076). Graft and patient survival rates were better, albeit not significantly, in the NLAT-M compared with PLAT-M recipients. CM status was investigated in 62/80 recipients, 18/62 recipients had positive CM (PCM), and 44 had negative CM (NCM). Five of 18 PCM recipients (28%) experienced early graft loss compared with 1/44 (2%) with NCM (p = 0.006). Rejection episodes were more frequent within first 3 months post-LT in PCM recipients compared with NCM (p = 0.015). One-year graft survival rate was better in NCM, compared with PCM recipients (graft loss of 2/44 vs 5/18). NCM PLAT-M had a higher incidence of rejection episodes compared with the NCM NLAT-M group (p = 0.031). The presence of anti-HLA antibodies suggests a deleterious effect on LT outcome, and was associated with an increased incidence of early graft loss and rejection episodes.

A short human and mouse MLR assay utilizing lymphokine (IL-2, IL-3) secretion as an early activation event

The mixed leukocyte reaction is the only functional in vitro assay currently employed for confirmation of MHC matching between bone marrow recipients and their prospective donors and for MHC class II (HLA-Dw) typing. This assay is, however, time-consuming (6 days for human MLR), whereas for clinical purposes results are often required much earlier. In an attempt to shorten the MLR incubation period, we tested IL-2 (in human MLR) and IL-2/IL-3 (in mouse MLR) production as an indication of early stages of T cell activation. We here describe a shorter assay in which IL-2 and IL-3 secretion during MLR was assessed by adding the respective lymphokine-dependent cell lines either to the MLR supernatants or directly to the original MLR cultures, using the colorimetric (3-[4,5 Dimethylthiazol-2-yl]-2.5-diphenyltetrazolium bromide) (MTT) technique or the 3H-thymidine incorporation assay. In both human and mouse MLR systems, lymphokine production peaked at 24–48 hr after culture initiation, allowing tests to be completed within 48 to 72 hr. Weak MLR responses, as detected by lymphokine production, could be considerably amplified by irradiating (250–1000 cGy) the responder cells and by adding heparin (1–10 U/ml) to the cultures. The results obtained by this novel procedure correlated with those obtained by the standard 6-day human MLR assay in over 250 combinations tested thus far, and therefore it may replace the standard MLR procedure.

Differential expression of HLA class-I antigens on B and T lymphocytes obtained from human lymphoid tissues

The amount of HLA class-I antigens was determined on the surface of enriched populations of B and T lymphocytes obtained from human peripheral blood, lymph nodes and spleens. The assays were performed using monoclonal antibodies that recognize different determinants on HLA class-I antigens and utilizing a simple and sensitive enzyme-linked immunosorbent assay (ELISA). Our results indicate that B lymphocytes obtained from human peripheral blood, lymph nodes and spleens express at least twice as many HLA class-I antigens as T lymphocytes obtained from the same organs.

Enzyme-linked immunosorbent assay for HLA determination on fresh and dried lymphocytes

HLA-A and -B antigens were detected on fresh and dried peripheral blood lymphocytes by an enzyme-linked immunosorbent assay. Intact cells fixed to plates with glutaraldehyde were used as antigen and anti-HLA alloantisera as a source of antibodies. Determination of HLA antigens by the ELISA technique was comparable with the complement-dependent cytotoxicity test. The relative stability of HLA antigens as shown in this report and the extensive polymorphism of the HLA system make the ELISA technique a promising tool for the analysis of HLA antigens on non-living cells including, for example, medicolegal investigation of blood stains.

Positivity in a modified mixed leukocyte reaction test correlates with molecular HLA-C disparity in prediction of unrelated bone marrow transplantation outcome

The modified mixed leukocyte reaction (MMLR) test consists of the standard MLR (SMLR) test to which interleukin-4 (IL-4) has been added. It is a sensitive procedure capable of detecting alloreactivity not detected by the SMLR. In the present study we applied the MMLR test to unrelated bone marrow transplantation (BMT) in an attempt to predict graft versus host disease (GVHD) and graft rejection (GR) by detecting alloreactivity between recipient/donor pairs otherwise found to be fully matched (HLA class I A and B tested by serology; class II DRB1 and DQB1 by sequence specific oligonucleotide probes [SSOP]) and by studying the relationship of MMLR alloreactivity and HLA-C disparity in the prediction of transplant related complications. Thirty-five patients transplanted from unrelated donors were included in the study. The MMLR test was seen to correlate with the incidence of transplant related complications, as of the 19 positive, cases 12 (63%) developed acute GVHD and 7 (37%) GR, while of the 16 negative cases only 5 (31%) developed GVHD (4 acute, 1 chronic) (p = 0.0001) and 2 (12.5%) GR. No such correlation was seen between the SMLR and the incidence of transplant related complications: the SMLR test was positive in only 4 (11%) cases (all of which developed GVHD or GR) but of the 31 negative cases 22 (71%) also developed GVHD or GR. Reactivity in the MMLR also correlated with molecular HLA-C disparity (p = 0.015): While of the 19 positive cases 10 (53%) had molecular HLA-C disparity, of the 16 cases with negative MMLR, 14 (87.5%) were matched for molecular HLA-C. Two-way analysis confirmed that patients with positive MMLR transplanted from HLA-C mismatched donors were more likely to develop post BMT complications, including GVHD and GR, than patients with negative MMLR transplanted from HLA-C matched donors (r = +0.70) (p = 0.001). We conclude that the MMLR test may be a useful tool in the prediction of transplant related complications such as GVHD and GR, post unrelated BMT. Moreover, the MMLR test, in conjunction with molecular HLA-C typing, may improve unrelated donor selection.

Cytokine production in human mixed leukocyte reactions performed in serum-free media.

The mixed leukocyte reaction (MLR) is an in vitro test commonly performed in a serum-containing medium (SCM), and used to study allorecognition and cellular immunity accompanied by cytokine release. We investigated the possibility of performing the MLR test in serum-free media (SFM) by comparing human leukocyte proliferation and cytokine release in MLRs performed in SFM and SCM. Of the four SFM tested, only Biotarget- was as effective as SCM in supporting leukocyte proliferation and IL-2 secretion. Both phenomena were observed only in allogeneic combinations. The levels of IL-1, IL-6, and TNFalpha in allogeneic MLR combinations in SFM were half those in SCM cultures; the kinetics of their release were the same. With the exception of IL-2, a high degree of spontaneous release of the other three cytokines analyzed was observed in responder cells, in irradiated stimulator cells, and in autologous combinations cultured in both SCM and SFM. It appears that unlike IL-2, the cytokines IL-1, IL-6, and TNFalpha are nonspecifically produced in MLR and cannot serve as sensitive indices of HLA disparity.

Zonal variation of HLA expression on human cornea epithelium.

Seven human corneas were studied, using the enzyme-linked immunosorbent assay (ELISA) technique, for expression of human leukocyte antigens (HLA) class-l and class-11 antigens on the epithelial cells of the central 8-mm corneal button and the remaining corneal periphery and limbus. The antigenicity was compared with that of Raji and Daudi cell lines, which served as controls. It was demonstrated that the epithelium of the two corneal parts shows a high expression of HLA class-I antigens, albeit not as strong as that found in the control cell lines. On the other hand. HLA class-11 antigens were found only in the limbal-peripheral area. Expression of the HLA class-1 antigens was weaker in the central portion of the cornea. It is proposed that the absence of HLA class-11 antigens expression in the central portion of the cornea offers an additional explanation for the greater success of small corneal grafts, since the recognition step necessary for the immunological response is lacking.

A sensitive and specific ELISA using monoclonal capture antibodies for the detection of HLA antigens in blood stains

A double antibody ELISA technique is described to detect HLA antigens in extracts of blood stains. The assay involves capture of free HLA determinants using an immobilized monoclonal antibody directed against monomorphic regions of HLA class I and HLA class II antigens. The captured antigens are then detected using alloantisera directed against the polymorphic regions of the captured HLA entities. The technique is able to detect specific HLA-A, B, and DR antigens in extracts prepared from blood smears as well as from dried and freshly thawed lymphocytes. The assay may be of potential use in forensic medicine, particularly in instances where extraction of nucleic acids for fingerprinting is not feasible.