Co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells attenuates human NK cell-mediated degranulation

Natural killer (NK) cells play an important role in immune rejection in solid organ transplantation. To mitigate human NK cell activation in xenotransplantation, introducing inhibitory ligands on xenografts via genetic engineering of pigs may protect the graft from human NK cell-mediated cytotoxicity and ultimately improve xenograft survival. In this study, non-classical HLA class I molecules HLA-E and HLA-G were introduced in an immortalized porcine liver endothelial cell line with disruption of five genes (GGTA1, CMAH, β4galNT2, SLA-I α chain, and β-2 microglobulin) encoding three major carbohydrate xenoantigens (αGal, Neu5Gc, and Sda) and swine leukocyte antigen class I (SLA-I) molecules. Expression of HLA-E and/or HLA-G on pig cells were confirmed by flow cytometry. Endogenous HLA-G molecules as well as exogenous HLA-G VL9 peptide could dramatically enhance HLA-E expression on transfected pig cells. We found that co-expression of HLA-E and HLA-G on porcine cells led to a significant reduction in human NK cell activation compared to the cells expressing HLA-E or HLA-G alone and the parental cell line. NK cell activation was assessed by analysis of CD107a expression in CD3-CD56+ population gated from human peripheral blood mononuclear cells. CD107a is a sensitive marker of NK cell activation and correlates with NK cell degranulation and cytotoxicity. HLA-E and/or HLA-G on pig cells did not show reactivity to human sera IgG and IgM antibodies. This in vitro study demonstrated that co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells provided a superior inhibition in human xenoreactive NK cells, which may guide further genetic engineering of pigs to prevent human NK cell mediated rejection.

Genetic engineering of porcine endothelial cell lines for evaluation of human-to-pig xenoreactive immune responses

Xenotransplantation (cross-species transplantation) using genetically-engineered pig organs offers a potential solution to address persistent organ shortage. Current evaluation of porcine genetic modifications is to monitor the nonhuman primate immune response and survival after pig organ xenotransplantation. This measure is an essential step before clinical xenotransplantation trials, but it is time-consuming, costly, and inefficient with many variables. We developed an efficient approach to quickly examine human-to-pig xeno-immune responses in vitro. A porcine endothelial cell was characterized and immortalized for genetic modification. Five genes including GGTA1, CMAH, β4galNT2, SLA-I α chain, and β2-microglobulin that are responsible for the production of major xenoantigens (αGal, Neu5Gc, Sda, and SLA-I) were sequentially disrupted in immortalized porcine endothelial cells using CRISPR/Cas9 technology. The elimination of αGal, Neu5Gc, Sda, and SLA-I dramatically reduced the antigenicity of the porcine cells, though the cells still retained their ability to provoke human natural killer cell activation. In summary, evaluation of human immune responses to genetically modified porcine cells in vitro provides an efficient method to identify ideal combinations of genetic modifications for improving pig-to-human compatibility, which should accelerate the application of xenotransplantation to humans.

Effect of Treatment With Tabalumab, a B Cell-Activating Factor Inhibitor, on Highly Sensitized Patients With End-Stage Renal Disease Awaiting Transplantation

B cell-activation factor (BAFF) is critical for B cell maturation. Inhibition of BAFF represents an appealing target for desensitization of sensitized end-stage renal disease (ESRD) patients. We conducted a Phase 2a, single-arm, open-label exploratory study investigating the effect of tabalumab (BAFF inhibitor) in patients with ESRD and calculated panel reactive antibodies (cPRAs) >50%. The treatment period duration was 24 weeks. Eighteen patients received tabalumab, at doses of 240-mg subcutaneous (SC) at Week 0 followed by 120-mg SC monthly for 5 additional months. Patients were followed for an additional 52 weeks. Immunopharmacologic effects were characterized through analysis of blood for HLA antibodies, BAFF concentrations, immunoglobulins, T and B cell subsets, as well as pre- and posttreatment tonsil and bone marrow biopsies. Significant reductions in cPRAs were observed at Weeks 16 (p = 0.043) and 36 (p = 0.004); however, absolute reductions were small (<5%). Expected pharmacologic changes in B cell subsets and immunoglobulin reductions were observed. Two tabalumab-related serious adverse events occurred (pneumonia, worsening of peripheral neuropathy), while the most common other adverse events were injection-site pain and hypotension. Three patients received matched deceased donor transplants during follow-up. Treatment with a BAFF inhibitor resulted in statistically significant, but not clinically meaningful reduction in the cPRA from baseline (NCT01200290, Clinicaltrials.gov).

New crossmatch technique eliminates interference by humanized and chimeric monoclonal antibodies

Humanized and chimeric antilymphocyte antibodies (Ab) are used to prevent and treat rejection and for treatment of human disease. Rituximab (RIT, anti-CD20), daclizumab (DAC; anti-CD25), alemtuzumab (ALE; anti-CD52), or infliximab (IFX) may interfere with Ab detection methods such as complement-dependent cytotoxicity (CDC) and flow cytometric crossmatch (FCXM). These agents are recognized as anti-human Ab or fix complement and are not differentiated from anti-allo-Ab. A new enzyme-linked immunosorbent assay crossmatch (XM) utilizing class I and II HLA antigens from donor cells called Transplant Monitoring System (TMS; GTI, Waukesha, Wisc) potentially precludes interference by eliminating non-major histocompatability complex antigens. To test this, normal sera (nonsensitized volunteers) were supplemented with 0.1 or 10 microg/mL of RIT, DAC, IFX or ALE, and were tested using three methods: the TMS T-cell CDCXM with antihuman globulin (AHG); and B-cell CDCXM without AHG; and FCXM with mean channel shifts of 45 and 150 indicating positive T-cell and B-cell crossmatch, respectively. No reactivity occurred with normal sera using any crossmatch technique. At 0.1 and 10 microg/mL, RIT interfered with CDC B-cell, but not T-cell crossmatch. RIT at 10, but not 0.1 microg/mL interfered with B-cell FCXM. No interference occurred with RIT in T-cell FCXM or TMS. ALE interfered with B-cell and T-cell CDC and FCXM but neither class I nor II TMS. DAC did not interfere with CDC or FCXM at 0.1 microg/mL, but gave false positive B-cell FCXM and CDCXM with some samples. No interference by DAC occurred using TMS. TMS may be useful to differentiate de novo donor-specific Ab after treatment with humanized or chimeric Ab.

Detection of IGA anti-OKT3 antibodies in OKT3-treated transplant recipients

Murine OKT3 monoclonal antibodies function as an immunosuppressant drug for organ transplant recipients. A contraindication to retreatment may develop, however, because a high proportion of OKT3-treated patients form anti-OKT3 antibodies. Previous data have shown that only antiidiotypic IgG antibodies can negate the beneficial effect of the drug. Eighty-two OKT3-treated transplanted patients were tested by ELISA for IgG, IgK and IgA anti-OKT3 antibodies and compared with 200 controls. The anti-OKT3 antibody-positive sera were screened additionally by flow cytometry for the presence of antiidiotypic activity by measuring Ortho OKT3-FITC activity on a CD3-positive cell line, Jurkat, before and after incubation with serial dilutions of patient and control sera. Forty-four of 82 patients developed antibodies to OKT3, 20 manifested IgG, 20 produced both IgG and IgA, and 4 IgA only. We never detected IgM anti-OKT3. Of the 44 anti-OKT3-positive patient sera, 25 showed antiidiotypic specificity. Two IgG/IgA anti-OKT3-positive patient sera were IgG-depleted by Protein G. Both continued to exhibit antiidiotypic IgA activity. IgA anti-OKT3 was associated with low serum OKT3 levels and lack of ability of OKT3 to lower total CD3 cell numbers to therapeutic levels. This is the first report of IgA anti-OKT3 antibody in transplant recipients. Isotype IgA anti-OKT3 was observed in 54% of the patients whose sera tested positive for anti-OM by ELISA. The IgG/ IgA anti-OKT3-positive patient sera tested continued to exhibit antiidiotypic OKT3 reactivity when depleted of IgG. We urge that OKT3-treated patients be monitored routinely for IgA anti-OKT3 antibodies to avoid the expense and potential complications of retreatment with this drug in sensitized patients.

Phenotypic characterization of normal human placental mononuclear cells

The placenta is a rich source of immunocompetent cells. We have studied the phenotype, number and origin of placental mononuclear blood cells isolated from 32 normal term placentae using 4 color flow cytometry. Respective maternal and cord blood leucocyte preparations were also compared. Placental tissue without extraembryonic membranes was cut into small pieces and divided. One portion was washed extensively with ice-cold PBS. Both tissue portions were disrupted in a blender and cells were dissociated by using a 180 mu sieve. Leucocytes were isolated by Ficoll-Hypaque density gradient centrifugation. Maternal and cord bloods were HLA typed and in cases of HLA-A2 or B7/40 disparity, monoclonal anti-HLA antibodies to these antigens showed that unwashed placental tissue contained 35% maternal and 65% fetal cells. This ratio, however, was not reflected for a given cell phenotype. In comparison, washed placental tissue contained cells of fetal origin only. Both unwashed and washed placental tissue contained fewer CD3 and CD4, but more CD8 cells than maternal and cord blood. Markers of NK cells such as, CD16, CD56, and CD57 showed this cellular phenotype to be 15 times more abundant in the placental preparations than in cord and maternal blood. The quantitative differences between peripheral blood and placental CD8 and NK cells were further explored with an antiprogesterone receptor antibody in combination with anti-CD8, anti-CD57 and anti-HLA-DR. The number of progesterone receptor (PGR) positive cells was three times higher in placental tissues than in cord or maternal blood. These data indicate that the phenotypic frequencies of certain placental leucocytes are significantly different from maternal and fetal peripheral blood. Progesterone and the presence of PGR may be important in the differential retention of placental leucocytes.