Immunochemical analysis of anti-HLA-A2, HLA-A3, and HLA-B27 xenoantisera elicited with hybrids between human and murine cells

Human Neuroblastoma Cells Trigger an Immunosuppressive Program in Monocytes by Stimulating Soluble HLA-G Release

HLA-G is overexpressed in different tumors and plays a role in immune escape. Because no information is available on HLA-G in relation to human neuroblastoma, we have investigated the expression of membrane-bound and secretion of soluble isoforms of HLA-G in neuroblastoma and functionally characterized their immunosuppressive activities. At diagnosis, serum soluble HLA-G (sHLA-G) levels were significantly higher in patients than in age-matched healthy subjects. In addition, patients who subsequently relapsed exhibited higher sHLA-G levels than those who remained in remission. Neuroblastoma patient sera selected according to high sHLA-G concentrations inhibited natural killer (NK) cell and CTL-mediated neuroblastoma cell lysis. Such lysis was partially restored by serum depletion of sHLA-G. In 6 of 12 human neuroblastoma cell lines, low HLA-G surface expression was not up-regulated by IFN-gamma. Only the ACN cell line secreted constitutively sHLA-G. IFN-gamma induced de novo sHLA-G secretion by LAN-5 and SHSY5Y cells and enhanced that by ACN cells. Primary tumor lesions from neuroblastoma patients tested negative for HLA-G. Neuroblastoma patients displayed a higher number of sHLA-G-secreting monocytes than healthy controls. Incubation of monocytes from normal donors with IFN-gamma or pooled neuroblastoma cell line supernatants significantly increased the proportion of sHLA-G-secreting cells. In addition, tumor cell supernatants up-regulated monocyte expression of CD68, HLA-DR, CD69, and CD71 and down-regulated IL-12 production. Our conclusions are the following: (a) sHLA-G serum levels are increased in neuroblastoma patients and correlate with relapse, (b) sHLA-G is secreted by monocytes activated by tumor cells rather than by tumor cells themselves, and (c) sHLA-G dampens anti-neuroblastoma immune responses.

Serum levels of beta-2-microglobulin-free heavy chain of HLA class I antigen in healthy individuals: relationship to their class I allotype

An ELISA-based double determinant immunoassay has been established to measure the soluble beta2-microglobulin (beta2m)-free heavy chain (FHC) of the HLA-B, -C (and HLA-A3, -A28 and -A30) class I molecular complex in sera from 212 HLA-typed healthy unrelated individuals. FHC was calculated by means of a standard curve constructed using serial concentrations of beta2m-associated HLA-class I heavy chain (HLA-I)/FHC purified from cultured human lymphoid cell C1R-sB7-supernatant. The mean FHC concentration (+/-SD) was 0.25 mg/l (+/-0.2). Its median concentration did not statistically differ between males and females, though the male/female ratio was greater in the high secretor (FHC >0.45 mg/l; mean + 1SD) than in the low secretor group (FHC < 0.05 mg/l; mean - 1SD). FHC < 0.05 mg/l was statistically (Fisher's exact test) associated with HLA-B17 (p = 0.003); FHC > 0.45 mg/l was statistically associated with HLA-B35 (p = 0.003) and -Cw4 (p = 0.002). None of these allele-positive groups showed a mean FHC concentration 1.5 times higher than that of the corresponding allele-negative ones. This allotype-dependent HLA-B and C FHC enhancement was less marked than that previously reported for HLA-I in individuals carrying HLA-A9 (and its splits). These results indicate that FHC could be a more valuable marker when its levels are compared among individuals carrying different allotypes. Moreover the lack of correlation between FHC and HLA-I levels measured in 52 HLA-A3, -A28 or -A30 positive individuals suggests that the two molecules may be regulated by different metabolic pathways and their serum expression may have a different biological significance.

Increased serum levels of beta2m-free HLA class I heavy chain in multiple myeloma

Serum levels of beta2-microglobulin (beta2m)-free HLA class I heavy chain (FHC) in 94 patients with multiple myeloma (MM) were higher than in 29 patients with monoclonal gammopathy of undetermined significance (MGUS) (P = 0.023) and in 97 sex- and age-matched healthy controls (P < 0.0001). Spearman correlation analysis indicated that in MM, FHC correlated with beta2m (r = 0.31, P = 0. 003) and the percentage of bone marrow plasma cells (BMPC%) (r = 0. 36, P = 0.002), whereas beta2m, in addition to BMPC% (r = 0.43, P = 0.0003), also correlated with creatinine levels (r = 0.63, P < 0.0001), haemoglobin levels (r = -0.35, P = 0.0007) and patient age (r = 0.34, P < 0.0011). Furthermore, MM patients with poor prognosis (beta2m >/= 6 mg/l) displayed higher FHC levels than those with a better prognosis (beta2m < 6mg/l) (P < 0.021). At variance from beta2m, these levels were not influenced by renal failure, as indicated by the lack of Spearman correlation of FHC with creatinine concentration and of statistical significance between the median FHC concentration of MM patients with creatinine < 176.6 micromol/l and those with creatinine >/= 176.6 micromol/l (P = 0.3). Stratification of patients according to disease activity and stage showed that FHC levels were only statistically different (P = 0.04) for disease activity, whereas beta2m and C-reactive protein were not. Taken together, our data indicate that serum FHC may be a useful disease marker in MM.

Analysis of the repertoire of anti-HLA antibodies with anti-idiotypes to a murine anti-HLA-A2,A28 monoclonal antibody

Xenoantibodies to idiotypes of the anti-HLA-A2,A28 MoAb CR11 -351 were isolated from an antiserum raised in rabbit #81 by immunizations with purified MoAb CR11 -351. The purification procedure involved absorption with insolubilized mouse immunoglobulins and monoclonal antibodies and affinity chromatography on insolubilized MoAb CR11 -351. Two antibody populations were identified in the xenoantibody preparation #81: one recognizes a recurrent idiotope expressed by the MoAb CR10 -215, CR10 -402, Q1/28, Q6 /64, and 6/31 to monomorphic determinants of HLA-A,B antigens and by the MoAb CR10 -343, CR11 -462, and Q5/6 to human Ia antigens. The other antibody population recognizes a private idiotope. Neither idiotope was detected on the anti-HLA-A2,A28 variant (A28) MoAbs BB7 .2, MA2 .2, and PA2.1, on the anti-HLA-A2,B17 MoAb MA2 .1 and on antibody populations in conventional anti-HLA-A2,A28 antisera. The idiotopes were also not detected on the anti-HLA-A2,A28 MoAb A2,A28 M1 which recognizes a determinant spatially close to that identified by the MoAb CR11 -351. The idiotope(s) recognized by the xenoantibodies #81 may be located in the combining site of the MoAb CR11 -351, since its incubation with the anti-idiotype antibodies specifically blocks the reactivity with lymphoid cells with the appropriate HLA phenotype.

HLA class I specific T lymphocyte clones with dual alloreactive functions

Four human T lymphocyte clones exhibiting proliferative responses to class I HLA antigens were isolated from an in vitro mixed lymphocyte culture (MLC). Three clones expressed the Leu-2+3- phenotype and demonstrated proliferation in response to HLA-B8, while the fourth clone expressed the Leu-2-3+ phenotype and proliferated in response to HLA-A2. These clones were also cytotoxic towards cells bearing the same target antigens. Blocking studies utilizing monoclonal antibodies demonstrated that proliferation was triggered by determinants on the class I molecule itself, and these determinants appear to be spatially close to those which determine serologic allospecificity. These findings support the concept that the class I molecules themselves are the weak MLC stimulating determinants previously mapped to the HLA-A and B regions of the major histocompatibility complex.

The monoclonal antibody CR11-351 discriminates HLA-A2 variants identified by T cells

Serologic and immunochemical assays have shown that the monoclonal antibody (MoAb) CR11-351 recognizes a determinant expressed by HLA-A2 and A28 alloantigens. The MoAb CR11-351 blocks the cytotoxicity of some, but not all, anti-HLA-A2 and anti-HLA-A28 alloantisera tested. These findings suggest that each allospecificity consists of several determinants, only some of which are spatially close to the determinant defined by the MoAb CR11-351. The binding of the MoAb CR11-351 to HLA-A2 lymphoid cells is not effected by their precoating with the HLA-A, B-specific MoAb CR10-214, Q6/64, and 6/31 but is enhanced by at least 20% by the MoAb CR10-131, CR10-402 and by the beta 2-m-specific MoAb NAMB-1. The MoAb CR11-351 did not react with one of four HLA-A2 variants which are indistinguishable with conventional anti-HLA-A2 sera, but are not recognized by "normal" HLA-A2-restricted cytotoxic T cells and possess structurally distinct HLA-A2 heavy chains. Therefore the MoAb CR11-351 provides the first evidence of a serologically detectable difference between the four HLA-A2 variants and "normal" HLA-A2 antigens.

The monoclonal xenoantibody Q6/64 recognizes a determinant expressed by certain gene products of the A and B loci of the HLA region

A combination of serological (cytotoxicity, binding assay, lysostrip) and immunochemical (indirect immunoprecipitation, sequential immunoprecipitation, two-dimensional gel electrophoresis) assays have shown that the monoclonal antibodies Q6/64 recognizes an antigenic determinant which is expressed by certain gene products of the A and b loci of the HLA region. The determinant identified by Q6/64 is spatially close to those which define the serological polymorphism of the HLA-A, B, C antigenic system. The results presented in this study in conjunction which those recently published by other investigators indicate that sharing of determinants among HLA-A and -B allospecificities is more frequent than originally assumed on the basis of the cross-reactivity pattern obtained with alloantisera. This conclusion is in agreement with the high degree of homology in the primary amino-acid sequence of A and B allospecificities.