Immunochemical analysis of a recombinant, genetically engineered, secreted HLA-A2/Q10b fusion protein

The turnover kinetics of major histocompatibility complex peptides of human cancer cells

Peptides presented by the major histocompatibility complex (MHC) are derived from the degradation of cellular proteins. Thus, the repertoire of these peptides (the MHC peptidome) should correlate better with the cellular protein degradation scheme (the degradome) than with the cellular proteome. To test the validity of this statement and to determine whether the majority of MHC peptides are derived from short lived proteins, from defective ribosome products, or from regular long lived cellular proteins we analyzed in parallel the turnover kinetics of both MHC peptides and cellular proteins in the same cancer cells. The analysis was performed by pulse-chase experiments based on stable isotope labeling in tissue culture followed by capillary chromatography and tandem mass spectrometry. Indeed only a limited correlation was observed between the proteome and the MHC peptidome observed in the same cells. Moreover a detailed analysis of the turnover kinetics of the MHC peptides helped to assign their origin to normal, to short lived or long lived proteins, or to the defective ribosome products. Furthermore the analysis of the MHC peptides turnover kinetics helped to direct attention to abnormalities in the degradation schemes of their source proteins. These observations can be extended to search for cancer-related abnormalities in protein degradation, including those that lead to loss of tumor suppressors and cell cycle regulatory proteins.

Soluble donor HLA class I and beta 2m-free heavy chain in serum of lung transplant recipients: steady-state levels and increases in patients with recurrent CMV infection, acute rejection episodes, and poor outcome

We determined the concentration of donor sHLA/beta(2)m and total beta(2)m-free heavy chain (HC) in the serum of lung transplant recipients with ELISA assays. While we were unable to detect specific donor beta(2)m-free HCs due to a lack of available antibodies, we could determine if events that led to an increase in the release of beta(2)m-free HC also led to an increase in the release of donor sHLA/beta(2)m, particularly the 36 kDa, proteolytically cleaved form. We found that lung transplants constituitively release donor sHLA/beta(2)m at ng/ml levels. The levels (both of donor sHLA/beta(2)m and total beta(2)m-free HC) were significantly increased in CMV-sero-negative recipients (but not in CMV-sero-positive recipients) at the onset of post-transplant CMV disease. Acute rejection episodes were also associated with an increased release of donor sHLA/beta(2)m, but not of beta(2)m-free HC. However, in patients with particularly poor outcome (i.e., graft loss within 1 year) there was a significant release of beta(2)m-free HC. Analysis of one such patient showed a predominance of 36 kDa forms of donor-sHLA/beta(2)m. Our data are consistent with the hypothesis that the metalloproteinase that cleaves beta(2)m-free HC is active during uncontrolled CMV infection and acute rejection. However, recall responses to CMV and controlled immune responses to donor may result in little or no activation of sHLA class I release.

Effective use of donor MHC class I gene therapy in organ transplantation: prevention of antibody-mediated hyperacute heart allograft rejection in highly sensitized rat recipients

Immunologically sensitized recipients present one of the most critical problems in clinical organ transplantation today, since preformed antibodies rapidly destroy donor tissue expressing specific MHC class I antigens (Ag). Therefore, sensitized patients are either unable to receive a compatible organ, or experience a prolonged waiting period. In this study we examined the effectiveness of donor MHC class I gene therapy in preventing hyperacute rejection (HR) of rat heart allografts in passively sensitized recipients. Our gene therapy strategy to address this problem is based on the phenomenon that liver transplants, which resist antibody-mediated HR, produce soluble MHC class I Ag capable of neutralizing preformed antibodies and suppressing the immune response. To mimic this "liver effect," we used liposomes to transfect cultured recipient (Lewis-RT1.Al) hepatocytes with plasmid DNA encoding the soluble donor MHC class I Ag, RT1.Aa. Control or RT1.Aa-transfected hepatocytes were implanted intrasplenically into Lewis recipients 1 day prior to heterotopic ACI (RT1.Aa) heart transplantation and injection of 6 ml of anti-ACI hyperimmune serum (HIS). Results showed that nearly all recipients receiving ACI-specific HIS and control hepatocytes experienced HR, while none of the recipients receiving HIS and hepatocytes expressing soluble RT1.Aa developed HR. Furthermore, active immunosuppression by soluble RT1.Aa was evidenced by prolongation of allograft survival, compared with controls not receiving HIS. In summary, soluble donor-MHC class I Ag gene therapy can prevent antibody-mediated destruction associated with HR. Future development of a similar strategy in humans may significantly improve the results of clinical organ transplantation in immunologically sensitized recipients.

Specific sHLA in healthy donors and donor-specific sHLA in renal transplant patients

We studied cadaver kidney transplant recipients to determine if their serum levels of donor-specific class I sHLA correlated with graft outcome. Testing of sHLA was performed by an ELISA sandwich assay using allospecific monoclonal trapping antibodies and anti-beta2-mu detecting antibody. Sufficient sHLA sensitivity (<1 ng/ml) was achieved by using two synergistic trapping antibodies. Suitable antibodies were available for A2 and B7, and data were collected for these two antigens. Stability of these sHLA was determined in plasma and serum as were ranges of normal and background levels. Background levels varied substantially. Five A2- recipients of A2+ grafts and 5 B7- recipients of B7+ grafts were studied with appropriate sHLA levels measured pre-transplant and at intervals post-transplant. Graft outcome was assessed by serum creatinines, renal biopsies and/or therapy for rejection. In the 5 patients (3 A2- and 2 B7-) whose post-transplant donor-specific sHLA never exceeded immunological complications (e.g., post-operative ATN, ureteral obstruction) did not affect the correlation. In the 5 patients with post-transplant levels exceeding pre-transplant levels, subsequent evidence of rejection was observed. Periodic measurement of donor-specific sHLA should be a useful instrument for monitoring renal allograft rejection.

Direct Analysis of Viral-Specific CD8+ T Cells with Soluble HLA-A2/Tax11-19 Tetramer Complexes in Patients with Human T Cell Lymphotropic Virus-Associated Myelopathy

Human T cell lymphotropic virus-I (HTLV-I)-associated myelopathy is a slowly progressive neurologic disease characterized by inflammatory infiltrates in the central nervous system accompanied by clonal expansion of HTLV-I-reactive CD8+ T-cells. In patients carrying the HLA-A2 allele, the immune response is primarily directed to the Tax11-19 peptide. The frequency, activation state, and TCR usage of HLA-A2/Tax11-19 binding T cells in patients with HTLV-I-associated myelopathy was determined using MHC class I tetramers loaded with the Tax11-19 peptide. Circulating Tax11-19-reactive T cells were found at very high frequencies, approaching 1:10 circulating CD8+ T cells. T cells binding HLA-A2/Tax11-19 consisted of heterogeneous populations expressing different chemokine receptors and the IL-2R β-chain but not the IL-2R α-chain. Additionally, Tax11-19-reactive CD8+ T cells used one predominant TCR Vβ-chain for the recognition of the HLA-A2/Tax11-19 complex. These data provide direct evidence for high frequencies of circulating Tax11-19-reactive CD8+ T cells in patients with HTLV-I-associated myelopathy.

HLA (A*0201) Mimicry by Anti-Idiotypic Monoclonal Antibodies

Soluble MHC Ags and anti-Id (anti-anti-MHC) Abs have both been shown to inhibit MHC alloantigen-specific B cell responses in vivo. We hypothesized that some anti-idiotypic Abs function as divalent molecular mimics of soluble HLA alloantigen. To test this idea, we studied two well-defined anti-idiotypic mAbs, T10-505 and T10-938, elicited in syngeneic BALB/c mice by immunization with CRll-351, an HLA-A2,24,28-specific mAb. Each anti-Id induced “Ab-3” Abs in rabbits that cross-reacted with HLA-A2 but not with HLA-B Ags. Furthermore, each anti-Id could bind to and block Ag recognition by Ha5C2.A2, a human homologue of mAb CRll-351. Both anti-Id mAb displayed weak reactivity with the human mAb SN66E3, which recognized an overlapping but distinct determinant of HLA-A2 Ags; neither reacted with human mAb MBW1, which recognized a nonoverlapping HLA-A2 determinant. Amino acid sequence comparison of mAb CRll-351 heavy and light chain variable region complementarity-determining regions (CDRs) with those of mAb Ha5C2.A2 and SN66E3 revealed short regions of homology with both human mAb; a large insert in the light chain CDR1 of mAb SN66E3 distinguished it from both CRll-351 and Ha5C2.A2. The amino acid sequences of mAb T10-505 and T10-938, which differed markedly from each other, revealed no homology to the α2 domain sequence of HLA-A*0201 that contains the CRll-351 mAb-defined epitope. We conclude that structurally different anti-Id Abs can mimic a polymorphic conformational epitope of an HLA Ag. In the case of T10-505 and T10-938 mimicry was not based on exact replication of the epitope by the hypervariable loops of the anti-Id mAb.

Soluble HLA class I in epithelial lining fluid of lung transplants: associations with graft outcome

We hypothesized that the small amounts of donor HLA-A and HLA-B proteins detected in the serum during organ allograft rejection are indicative of higher local releases within the graft itself. We determined the concentrations of total HLA class I (HLA-I) and, in selected cases, specific donor and host HLA-A and HLA-B proteins, in the epithelial lining fluid (ELF) sampled by bronchoalveolar lavage (BAL) of lung transplant recipients (n = 37) and of normal controls (n = 25). We found that 1) HLA-I proteins were enriched in the lung ELF relative to other proteins; 2) the concentration of HLA-I in the ELF of well-functioning transplants was similar to that in normal lungs; 3) HLA-I proteins and total proteins were elevated in the ELF of patients who developed chronic rejection or refractory acute rejection; 4) the concentration of HLA-I was correlated with the percentage of neutrophils but not with the percentage of lymphocytes in the ELF of transplanted lungs; and 5) only the percentage of lymphocytes was elevated in the ELF of transplant patients with active CMV infections. Total HLA-I from the ELF was found to contain a mixture of both donor- and recipient-type HLA-A and HLA-B proteins and the donor-type HLA-A2 was found to be highly enriched in the ELF relative to serum.

Expression of human recombinant beta 2-microglobulin by Aspergillus nidulans and its activity

The light chain of HLA class I protein (beta 2m) has been expressed in Aspergillus nidulans. The cDNA of beta 2m was modified using the polymerase chain reaction to include overlapping extensions for its subsequent fusion into an Aspergillus vector. This fusion resulted in beta 2m cDNA being flanked by the Aspergillus awamori glucoamylase promoter and the Aspergillus niger glucoamylase terminator. Expression of beta 2m was induced by the addition of starch to the culture medium. In preliminary mass culture trials, 177 micrograms/liter of f beta 2m were obtained in 60-liter fermentations. N-terminal sequencing of purified human beta 2m produced in fungi (f beta 2m) revealed that 28% of the purified protein was of proper sequence and 61% of the protein had an additional serine and lysine residue derived from the C-terminus of the fungal leader. Purified f beta 2m from culture supernatants appeared biochemically similar to beta 2m obtained from human urine (u beta 2m) as seen in immunoblot analysis. Functionally, f beta 2m effectively interacted as a subunit of class I MHC molecules. This was seen both in a sandwich ELISA for detecting properly folded HLA class I heavy chain and in assays showing cell-surface beta 2m exchange into the mouse class I MHC H-2Kd. In these experiments the biological activity of f beta 2m was indistinguishable from u beta 2m. The successful expression of biologically active beta 2m in A. nidulans suggests that fungal systems might be useful for the production of other active components of the HLA class I MHC complex.

Monitoring of kidney and simultaneous pancreas-kidney transplantation rejection by release of donor-specific, soluble HLA class I

Using an HLA-A2-specific ELISA we monitored daily pretransplantation and posttransplantation sera from five kidney and eight simultaneous pancreas-kidney HLA-A2-negative recipients of HLA-A2-positive transplants during hospitalization. We found that, unlike liver transplants, neither kidney nor simultaneous pancreas-kidney transplants continuously secreted donor HLA proteins. However, three of four rejection episodes in kidney recipients and seven of seven rejection episodes in simultaneous pancreas-kidney recipients were accompanied by elevated serum levels of donor sHLA-A2 (> 5 ng/ml). In only one kidney patient was there a release of donor antigen without evidence of rejection, but in the simultaneous pancreas-kidney group most patients had at least one time point of detectable sHLA-A2 without strong evidence of kidney rejection. While total sHLA levels were also elevated during rejection, the rise in donor-specific sHLA was more dramatic when compared to pretransplantation background levels. We hypothesized that the release of donor sHLA class I proteins by transplanted organs might be a systemic indication of rejection in both pancreas and kidney allografts. The detection of donor sHLA in recipient sera could be an important noninvasive monitor of rejection, especially in the pancreas, which is currently difficult to monitor as a single-organ transplant.

Epitope fine specificity of human anti-HLA-A2 antibodies. Identification of four epitopes including a haptenlike epitope on HLA-A2 at lysine 127

Anti-HLA-A2 CREG antibodies were purified from seven individuals by affinity chromatography. The binding of the purified antibodies to single or multiple amino acid variants of HLA-A2.1 was measured with an inhibition RIA. Substitutions at 10 amino acid residues in the polymorphic alpha 1 and alpha 2 domains were important for human antibody binding; eight of these have previously been shown to be important in the binding of murine anti-HLA-A2 CREG antibodies. Unlike any previously reported murine mAbs, the binding of antibodies from two individuals was eliminated by a substitution at the HLA-A2, -24, -28 shared loop amino acid residue lysine 127. Conversely, when the asparagine at residue 127 on the non-cross-reactive HLA-A3 was replaced with lysine, antibody binding was completely restored. The results further suggest that both lambda- and kappa-containing human antibodies that bind to this region may recognize lysine 127 as a haptenlike epitope. Anti-HLA-A2 antibodies that recognized a conformational epitope defined by changes at glycine 62 in the alpha 1 domain were predominated by lambda light chains whereas those that recognize an epitope defined by a loop residue at tryptophan 107 in the alpha 2 domain were predominated by kappa light chains. The data are consistent with a model of restricted epitope recognition of HLA-A2 by human B cells that is similar to, but distinct from, epitope recognition by mouse B-cell hybridomas, and may help to explain the phenomenon of public or cross-reactive idiotypes in the HLA system.

Activation of HLA-A2-specific memory B cells in severe combined immunodeficient mice

Peripheral blood leukocytes of all five HLA-A2-sensitized patients produced significant levels of human IgG (> or = 0.25 micrograms/ml) following polyclonal activation in vitro, but PBLs from only one patient (K.H.) who had been transfused recently (< 4 weeks) produced detectable anti-HLA-A2 IgG. PBLs from this in vitro responder and from one in vitro nonresponder (L.G.) were transferred intraperitoneally into SCID mice. A low level (range, 5-40 ng/ml) of human anti-HLA-A2 IgG was detected in the serum of the mice without additional stimulation. This anti-HLA-A2 IgG response was boosted (range, 40-200 ng/ml) when mice received a human skin xenograft or an early challenge with x-irradiated human leukocytes intraperitoneally. Although the anti-HLA antibodies produced were specific for HLA-A2, the boosting of anti-HLA-A2 IgG production did not require the expression of the HLA-A2 protein, since either HLA-A2-negative skin xenografts or HLA-identical x-irradiated PBLs enhanced the production of anti-HLA-A2 IgG. Dose-response of transferred PBLs and kappa:lambda composition of individual mouse anti-HLA-A2 production suggested that low-frequency human memory B-cell clones were stimulated to proliferate and/or triggered to become high Ab secretors by skin graft or PBL boost.