A phase I/II randomized open-label multicenter trial of efalizumab, a humanized anti-CD11a, anti-LFA-1 in renal transplantation

Leukocyte function associated antigen-1 (LFA-1) has a multifaceted role in the immune response, including adhesion and trafficking of leukocytes, stabilizing the immune synapse of the MHC-TCR complex and providing costimulation signals. Monoclonal antibodies to the CD11a chain of LFA-1 have been seen to result in effective immunosuppression in experimental models. Efalizumab, a humanized IgG1 anti-CD11a, is approved for use in psoriasis and may provide effective immunosuppression in organ transplantation. Thirty-eight patients undergoing their first living donor or deceased renal transplant were randomized to receive efalizumab 0.5 or 2 mg/kg weekly subcutaneously for 12 weeks. Patients were maintained on full dose cyclosporine, mycophenolate mofetil and steroids or half dose cyclosporine, sirolimus and prednisone. At 6 months following transplant patient survival was 97% and graft survival was 95%. Clinical biopsy-proven acute rejection in the first 6 months after transplantation was confirmed in 4 of 38 patients (11%). Three patients (8%) developed post transplant lymphoproliferative disease, all treated with the higher dose efalizumab and full dose cyclosporine. The two doses of efalizumab resulted in comparable saturation and modulation of CD11a. This phase II trial suggests that efalizumab may warrant further investigation in transplantation.

Effects of administration of a single dose of a humanized monoclonal antibody to CD11a on the immunobiology and clinical activity of psoriasis

BACKGROUND

CD11a/CD18 comprise subunits of leukocyte function associated antigen (LFA-1), a T-cell surface molecule important in T-cell activation, T-cell emigration into skin, and cytotoxic T-cell function.

OBJECTIVE

We explored the immunobiologic and clinical effects of treating moderate to severe psoriasis vulgaris with a single dose of humanized monoclonal antibody against CD11a (hu1124).

METHODS

This was an open label study with a single dose of hu1124 at doses of 0.03 to 10 mg/kg. Clinical (Psoriasis Area and Severity Index [PASI]) and immunohistologic parameters (epidermal thickness, epidermal and dermal T-cell numbers, and keratinocyte intercellular adhesion molecule 1 [ICAM-1] expression) were followed.

RESULTS

Treatment with hu1124, at doses higher than 1.0 mg/kg (group III), completely blocks CD11a staining for at least 14 days in both blood and psoriatic plaques. At 0.3 to 1.0 mg/kg, T-cell CD11a staining was completely blocked; however, blockade lasted less than 2 weeks (group II). Only partial saturation of either blood or plaque cellular CD11a was observed at doses of hu1124 between 0.01 and 0.1 mg/kg (group I). This pharmacodynamic response was accompanied by decreased numbers of epidermal and dermal CD3(+) T cells, decreased keratinocyte and blood vessel expression of ICAM-1, and epidermal thinning. Statistically significant drops in PASI compared with baseline were observed in group II patients at weeks 3 and 4 and in group III patients at weeks 2 through 10. No significant drop in PASI score was observed in group 1. Adverse events were mild at doses of 0.3 mg/kg or less and included mild chills, abdominal discomfort, headache, and fever. At a single dose of 0.6 mg/kg or higher, headache was the most common dose-limiting toxicity observed.

CONCLUSION

Targeting CD11a may improve psoriasis by inhibiting T-cell activation, T-cell emigration into the skin, and cytotoxic T-cell function.

Survival of human parathyroid tissue xenotransplanted in nude mice after 9 to 55 months' cryopreservation

Survival of human parathyroid tissue xenotransplanted after cryopreservation was studied. Peroperative biopsies from 26 patients were cryopreserved and xenotransplanted into nude mice after 9 to 55 months. At 8 to 12 weeks after transplantation, the morphology of the transplanted tissue was compared to that of the original tissue after thawing and before transplantation. Morphologically viable tissue was observed in 20 out of 26 nude mice (77%). Based on the morphological appearance, the parathyroid transplants were arranged into four "quality" groups. No correlation existed between the quality of the transplants and duration of storage, or between the age and sex of the patients. There was no correlation between initial clinical diagnosis or histopathological patterns (primary, secondary and tertiary hyperplasia [n=16], adenoma [n=9], one case undetermined) and transplant survival. After thawing and transplantation, all parathyroid grafts, except one, were morphologically either of the same or somewhat lower quality.

A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation

The efficacy of murine monoclonal anti-interleukin 2 alpha chain receptor (Tac) antibodies is limited by a short half-life and the development of antibodies to the heterologous protein. The safety, pharmacokinetics-dynamics, and immunosuppressive effect of a humanized anti-Tac antibody (HAT) was evaluated in 12 renal transplant recipients. Ten patients received living related transplants (three HLA-identical matches and seven one-haplotype or zero-haplotype matches) and two patients received cadaver organs. The patients were divided into four HAT treatment arms: 0.5 mg/kg/week (n=4), 1 mg/kg/week (n=2), 0.5 mg/kg every other week (n=3), and 1 mg/kg every other week (n=3). The first dose of HAT was given within 12 hr before transplantation, and four additional doses were given after transplantation. Patients were also placed on cyclosporine, steroids, and azathioprine. Only one patient, a recipient of a cadaver kidney in the lowest HAT treatment arm, had a reversible rejection episode. The 10 recipients of living related transplants were compared with 17 historical controls treated with an identical immunosuppressive regimen except for HAT. Whereas none of the HAT-treated living related donor recipients had a rejection episode, 6 of 17 (41%) of the historical controls had a rejection episode in the first year after transplantation. There were no first-dose reactions after HAT therapy or other subsequent side effects. None of the patients experienced opportunistic infections or malignancies. One patient developed low-titer anti-HAT antibodies, although the patient maintained high serum HAT concentrations throughout the study. Immune monitoring showed that there were no changes in the percentage or absolute counts of CD3 cells or T-cell subsets after HAT therapy. However, there was a significant decrease in the number of circulating lymphocytes that expressed free Tac. The overall harmonic mean half-life of HAT was 273 hr. The results of this study indicate that HAT given at 1 mg/kg every other week for a total of five doses may provide therapeutic HAT concentration levels and result in good saturation of Tac receptors for at least 12 weeks after transplantation. In summary, HAT is safe and is well tolerated by patients. Its long half-life and lack of immunization could make it a very useful immunosuppressive drug.

Long-term engraftment following in utero T cell-depleted parental marrow transplantation into fetal rhesus monkeys

A major concern with allogeneic BMT for treating most inherited diseases is the need to overcome graft rejection with conditioning chemotherapy which is associated with a relatively high morbidity and mortality. This can be eliminated if the transplant is done in utero when the fetus is unable to reject donor hematopoietic stem cells (HSC). We studied the efficacy of T cell-depleted (TCD) parental bone marrow as a source of HSC for transplantation into early gestation non-defective fetal rhesus monkeys. Thirteen opposite sexed TCD transplants were done into 44 day fetal recipients and 12 into 61 day recipients (165 day total gestation). The procedure-related mortality was 8%, all in the earlier age group. The overall survival was 60% at birth with a projected survival of 44 +/- 10% at 1.5 years with no difference between the two age groups. We used a PCR assay for the rhesus Y chromosome to detect male donor cells in female recipients (six animals transplanted at 44 days and five at 63 days). The overall engraftment rate was 73% with no difference as a function of gestational age at transplant. In six long-term surviving engrafted females we detected donor cells in the peripheral blood and bone marrow up to 3 years of age. We found a delay in the appearance of donor cells in the peripheral blood in engrafted animals, in some cases for up to 6 months post-BMT. In vitro mixed lymphocyte reaction and cell-mediated lymphocytotoxicity studies between the recipient and donor cells indicate that tolerance was induced to donor cells. Individual and pooled erythroid and myeloid marrow colonies grown in methyl cellulose were collected and analyzed for donor origin by PCR. The amount of donor cells in marrows from long-term engrafted animals was < 0.1%. In a fetal recipient studied at 35 days post-BMT, donor cells were detected in bone marrow and liver in both erythroid and myeloid lineages. These results indicate that TCD parental marrow can durably engraft in utero. While the engraftment rate is similar to that seen with fetal liver as the source of HSC, the degree of peripheral blood engraftment (percent donor cells) in this non-defective primate model is low. It will require increasing the percent pre-or postnatally for this approach to be clinically relevant in those disorders in which there is no selective survival advantage for normal engrafted donor cells.

The OKT3 Antibody Response Study: a multicentre study of human anti-mouse antibody (HAMA) production following OKT3 use in solid organ transplantation

Human anti-murine antibody titres following patient exposure to the monoclonal antibody Orthoclone OKT3 (muromonab-CD3) are determined by laboratories using diverse analytical methods which are not standardized and whose concordance is not established. A multicentre study group therefore compared testing for IgG anti-OKT3 antibody among seven laboratories. A set of 270 sera was obtained from 30 heart, 30 kidney and 30 liver transplant recipients with no previous exposure to OKT3 who were receiving OKT3 for induction immunosuppression. Sera were collected from each patient prior to and at 24 +/- 2 days and 31 +/- 2 days following initial OKT3 exposure. Identical aliquots of all 270 sera were tested for IgG anti-OKT3 antibody by each laboratory. In addition, the limit of detection of each laboratory's method was estimated by titration of an affinity-purified IgG anti-OKT3 reference material of known concentration. Anti-OKT3 antibody formation differed greatly among the three organ groups. Cardiac patients demonstrated the least sensitization and almost exclusively lower titres, while kidney recipients had more frequent and higher titre antibody formation. Liver recipients yielded the highest sensitization rate and the most frequent high titre sera. Importantly, the seven laboratories differed widely in the number of pretreatment sera reported as positive (ranging from 0% to 41% among laboratories), the number of post-OKT3 sera reported as positive (17-63%), the number of post-OKT3 samples with titre > or = 1000 (2-31%), and the number of patients sensitized 19-69%). Concordance among laboratories was highly variable, with interlaboratory agreement ranging from 38% to 83% on the sample titres assigned to 180 post-OKT3 sera. Many of the discordant results were consistent with differences in the limit of detection of the analytical methods, which ranged from 0.19 microgram/ml to > or = 15 micrograms/ml, a nearly 100-fold difference among laboratories. This study demonstrated the presence of both good concordance and significant discordance among laboratories in determining human anti-mouse antibody titres, and demonstrated that common titre categories (100, 1000, 10,000) were not equivalent among laboratories. The level of concordance among methods should be considered when comparing anti-OKT3 antibody results from different centres and their correlation with clinical events. Universal comparative testing, patterned after proficiency testing programmes, is needed to assess differences among laboratories and to bring uniformity and a sound interpretative basis to this field of testing.

Anti-tetanus toxoid antibody production after mismatched T cell-depleted bone marrow transplantation

We explored B-cell function after tetanus toxoid (TT) immunization in 12 children with severe combined immunodeficiency disease or leukemia who were long-term survivors of an HLA-matched sibling or haplocompatible T cell-depleted parental bone marrow transplant (BMT), 10 of their healthy donors, and 13 normal controls. Specific in vivo and in vitro anti-TT antibody (Ab) production were measured by ELISA. We studied donors' and recipients' peripheral blood mononuclear cells (PBMC) and mixed E- (non-T cells) and E+ cells (T cells) spontaneously and after stimulation by TT in the absence or presence of interleukin-2 (IL-2), IL-4, and IL-6. Five of the 12 patients and all donors and controls responded with in vivo anti-TT Ab. In vitro anti-TT Ab production correlated with the in vivo response. All seven of the nonresponders were either fully engrafted or mixed chimeras (donor T cells but autologous B cells and monocytes). We could not identify a T-cell defect in four of the five nonresponders who were tested. In contrast, E- cells from three of three responders cooperated with fresh donor E+ cells even when they shared only one HLA haplotype. In three of seven nonresponders, in vitro anti-TT Ab production was restored after the addition of IL-4 or IL-6 but not IL-2. Our results suggest that the humoral immunodeficiency that exists post mismatched T cell-depleted BMT is either a B-cell, a monocyte, or a B-cell/T-cell cooperation defect which, in some patients, may be correctible with the addition of a cytokine. Also, it is not necessary to engraft donor B cells to achieve normal antibody responses and the ability to respond does not appear to correlate with pretransplant chemotherapy.

Graft vs. host disease after liver transplantation in humans: a report of four cases

Four cases of patients in whom graft vs. host disease developed after liver transplantation are described. The clinical course of each patient was similar with fever, pancytopenia, diarrhea and a skin rash developing 1 or 2 mo after liver transplantation. The clinical diagnosis was made from skin or colon biopsy specimens. Liver dysfunction did not occur in the patients at the time of diagnosis. Extrahepatic donor DNA was identified in the three patients it was tested for. Three patients died from the complications of the disease primarily related to sepsis. The other patient recovered from the graft vs. host disease but died from lymphoproliferative disease.

Activation of class I HLA expression by TNF-alpha and gamma-interferon is mediated through protein kinase C-dependent pathway in CML cell lines

The combination of tumour necrosis factor alpha (TNF alpha) and gamma-interferon induced transcription of class I HLA genes in chronic myelogenous leukaemia (CML) cell lines through the formation of a complex between nuclear proteins and the transcriptional enhancers associated with these genes. Although gamma-interferon or TNF-alpha stimulated expression of class I HLA antigens in the EM2 and K562 CML cell lines when used alone, the effect of the combination of TNF-alpha and gamma-interferon was greater than that observed with either agent alone. The induction of class I HLA expression by gamma-interferon and TNF-alpha was inhibited completely by the isoquinoline sulfonamide H7, an inhibitor of protein kinase C. We conclude that the enhancement of the gamma-interferon induced transcriptional activation of class I HLA gene expression by TNF-alpha involves a protein kinase C-dependent pathway.

Improved results with combined donor-specific transfusion (DST) and sequential therapy protocol

A combined DST-sequential CyA therapy protocol has been described that results in optimum graft survival for 1- and 2-haplotype mismatched living related donor-recipient combinations. In addition to the excellent graft survival obtained through 4 years, lower prednisone and CyA dosage levels are achieved with significantly decreased infection rates during the posttransplant period.

A poorly differentiated lymphoma of donor origin in a renal allograft recipient

Malignant lymphoma is a frequent complication of organ transplantation. It has been suggested that such tumors arise as a result of uncontrolled proliferation of Epstein-Barr virus-infected B lymphocytes in an immunosuppressed host. Although a few cases of posttransplant lymphomas in bone marrow transplantation have been shown to be of donor cell origin, no recipients of solid-organ transplants are known to have developed lymphomas arising from donor cells. In this report, a case of diffuse high-grade lymphoma that apparently arose in the allograft of a renal transplant recipient is described. DNA fingerprinting demonstrated the tumor to be of donor origin; Epstein-Barr sequences were absent. A therapeutic trial consisting of withdrawal of immunosuppressive agents and administration of acyclovir was unsuccessful. These data support the notion that donor cells can undergo malignant transformation in solid-organ transplant recipients, and such tumors need not carry EBV genetic material.

Inability of cyclosporine to completely prevent the recurrence of focal glomerulosclerosis after kidney transplantation

From January 1984 through July 1986, 15 patients with biopsy-proven focal glomerulosclerosis (FGS) underwent kidney transplantation. Following transplantation, all patients were immunosuppressed with cyclosporine and prednisone. There were 8 men and 7 women with a mean age of 33 years (range, 16-47 years). Five patients (33%) had recurrence of FGS. Two patients had received kidneys from HLA identical siblings, and 3 patients were transplanted with cadaveric kidneys. In 4 out of 5 patients, the recurrence of FGS occurred within 3 months of transplantation. Of the 2 graft losses in this group, one was from recurrence of FGS. Ten patients followed for a mean of 25 months did not develop recurrence of FGS. No graft loss occurred in this group. Three patients with end-stage renal disease of unknown etiology were found to have FGS in the renal allograft and were presumed to have recurrence of FGS. All 3 patients developed the nephrotic syndrome following transplantation, and 1 patient has had progressive renal failure. Cyclosporine did not prevent the recurrence or the clinical manifestations of FGS following kidney transplantation. Additional studies are needed to determine if cyclosporine is effective in certain subgroups of patients with FGS.

Donor-specific blood transfusions versus cyclosporine--the DST story

DST provides excellent graft survival in one- and zero-haplotype-matched donor-recipient pairs as well as a trend towards improving graft survival in HLA-identical matches; serum creatinine levels are good in functioning grafts; Imuran coverage does appear to decrease DST sensitization to the blood donor in nonsensitized patients undergoing a first transplant, which encourages early DST and transplantation in this group; flow cytometry has been extremely helpful in excluding subliminal anti-class 1 antigen activity in patients with positive B warm crossmatches alone; DST, in itself, does not appear to preclude subsequent cadaveric transplantation in patients sensitized to their blood donor; and the family history of the blood donor is known, with essentially no risk to the recipients of hepatitis, AIDS, etc. In regards to the issue of whether DST or Cs is better, both have merits, and one must be aware of the circumstances that relate to the optimum application of each therapy. Only a prospective study of DST- and Cs-treated patients with a long-term follow-up will probably resolve the issue of the optimum regimen for one-haplotype-matched living related donor-recipient pairs. The ultimate strategy may involve the selective use of each regimen for the most appropriate circumstances.

The beneficial effect of pretransplant blood transfusions in cyclosporine-treated cadaver renal allograft recipients

212 cyclosporine-treated recipients of mismatched first cadaveric renal allografts are evaluated with respect to the effect of pretransplant random blood transfusions. It is determined that transfusions do not effect patient survival or morbidity. Pretransplant random blood transfusions correlate with significantly improved allograft success. There is also a trend, although not statistically significant, for further improvement of allograft survival with increasing numbers of transfusions. The transfusion effect is not related to the time at which the transfusions are given up to 2 years prior to transplantation. Transfused patients have a higher percent reactive antibody (PRA) than untransfused patients, but this does not cause them to wait for a cadaveric allograft significantly longer than the untransfused patients. Rejections are less severe in transfused patients. It is concluded that cyclosporine-treated recipients of first cadaveric renal allografts benefit from pretransplant blood transfusions.

Twenty years of renal transplantation in children

Two-hundred three children 1 to 16 years of age received kidney transplants during a 20-year period, 100 from living donors and 103 from cadaver donors. The overall survival rate was 79%. Actuarial patient and kidney survival rates at 15 years were 79% and 52%, respectively, for recipients of living donor kidneys and 57% and 19%, respectively, for recipients of cadaver donor kidneys. One of two children who received transplants in 1964 was alive 20 1/2 years later. Twenty-nine children had kidneys that had functioned more than 10 years; their mean serum creatinine concentration was 1.7 mg/dL and 24 were fully rehabilitated. Eighteen were more than 2 SD below the mean height of normal children, however. Comparison of survival rates during successive 5-year intervals showed significant improvement in patient survival during the 20-year period and smaller improvements in kidney survival after 1979. Patient survival after living donor transplants during the last 10 years was 100%, and kidney survival during the last 5 years was 92%. Improvement was attributed to the effect of experience, as well as to changes in immunosuppressive therapy in 1972 and the introduction of donor-specific transfusions in 1978.

A seven-year experience with donor-specific blood transfusions. Results and considerations for maximum efficacy

Two hundred thirty-nine transplants have been performed following donor-specific blood transfusions (DSTs) since 1978. Graft and patient survival in 1- and 0-haplotype-matched transplants with DST pretreatment is comparable to HLA-identical results through 4 years. Graft survival in 174 consecutive nondiabetic, non-HLA-identical DST recipients shows that the transfusion effect persists for at least 4 years, with graft survival of 88 +/- 3% at that time, compared with 83 +/- 4% in the concurrent HLA-identical group. Graft function, as determined by serum creatinine, was the same in both groups. Graft and patient survival in 20 0-haplotype matched pairs with DST pretreatment is 100% at 2 years. Low-dose Imuran coverage during DST administration (n = 91) was compared with a concurrent group with no Imuran (n = 93). Imuran had its maximum effect in patients undergoing their first transplant and with a pre-DST PRA less than 10% (12% vs. 21% sensitization rate in the no-Imuran group). Imuran did not appear to confer any beneficial effect in primary transplants with high PRAs and in patients undergoing a second or third transplant. The majority of patients formally excluded from transplantation because of a post-DST positive B-warm crossmatch can now be successfully transplanted with the use of flow cytometry analysis to rule out previously undetectable low levels of anti-T-lymphocyte antibodies. Of 62 patients with a positive B-warm crossmatch alone since 1982, 73% had a subsequent negative fluorescence-activated cell sorter (FACS) crossmatch permitting transplantation. Preliminary results of a DST and cyclosporine treatment study are described. In conclusion, a long-term immunologic effect of DST has been confirmed and the indications and considerations for optimum use of the DST protocol have been more clearly defined.

Effect of donor-specific transfusions on renal transplantation in children

Most family members who are evaluated as kidney donors for children have high reactivity in a mixed lymphocyte culture test and are thus excluded from donation. Fifty children, most of whom had highly reactive mixed lymphocyte cultures with their donors, were challenged with three blood transfusions from their donors before transplantation and were tested for the development of lymphocytotoxic antibodies. Ten children (20%) became sensitized and had a positive T-cell or B-cell crossmatch. Sensitization occurred less frequently in children treated with azathioprine during donor-specific transfusions (11%) than in those not treated (26%), but the difference was not significant. Thirty-seven children received renal transplants from their blood donors after the donor-specific transfusions. There were no deaths, and only two patients had kidney failure. Actuarial kidney survival was 93% after 6 years. The use of donor-specific transfusion has increased the number of related-donor transplants performed and the results have been highly successful.

Dramatic improvement in the success rate for renal transplants in diabetic recipients with donor-specific transfusions

The chance of achieving successful kidney transplants in diabetic patients was previously limited because few of them had optimally-matched (2-haplotype) related donors. Hence, transplants were usually not carried out until renal failure had already occurred. The application of donor-specific transfusions (DSTs) prior to transplantation to poorly matched donor-recipient pairs (1-haplotype) has been associated with a high success rate for type-I diabetic recipients in our center. The rate of graft survival for 35 consecutive transplants in this category was 88%, 80%, and 73% at 1, 2, and 5 years, respectively. Furthermore, the rate of patient survival was 94%, 90%, and 90% at 1, 2, and 5 years. These patient and graft survival data were without significant difference when compared with the corresponding data for 142 optimally-matched (2-haplotype) related transplants performed without DSTs for nondiabetic recipients, and also when compared with the corresponding data for 130 poorly matched (1 or 0-haplotype) related transplants involving nondiabetic recipients who were prepared for transplantation with DSTs. These good results with DSTs in diabetic recipients emphasize that earlier transplantation utilizing poorly matched related donors should be seriously considered for diabetic patients even before the onset of renal failure, as long as the transplants are carried out in association with DSTs.

Update of the University of California at San Francisco experience with donor-specific blood transfusions

Prospective pretreatment with deliberate DST has afforded MLC reactive related donor-recipient pairs enhanced opportunity for successful transplantation. The sensitization rate in patients receiving DST prior to primary transplantation was 30%, but this sensitization has been generally specific and narrow-those patients developing a positive DSXM do not appear to be jeopardized regarding later cadaver transplantation. Graft survival rates in 86 recipients of kidneys from their blood donors are 95% (1-year) and 93% (2-year). This graft survival rate appears to outweigh the minimal risk of possible unfavorable sensitization. Potentially unsuccessful transplants in immunologically disparate related donor-recipient pairs can be avoided, and the transplants actually performed have enhanced prospects of success.

Recurrent systemic lupus erythematosus involving renal allografts

Two cases of recurrent lupus erythematosus involving renal transplants are described. Neither case showed changes of transplant rejection. The clinical course, serologic tests, and renal histopathologic findings remarkably paralleled those seen during each patient's primary disease presentation. Typical and severe extrarenal manifestations of dermatitis, pleuritis, and polyarthritis were noted before renal allograft lupus involvement. Rapid renofunctional deterioration was halted in one patient by plasmapharesis. In the second patient a more protracted course involving the allograft is anticipated. Although previous experiences suggest that lupus disease activity "burns out" after the development of chronic renal failure, findings from these two cases argue against this presumption. Longer periods of transplant follow-up may show more recurrence of lupus erythematosus.

Early-onset pauciarticular juvenile rheumatoid arthritis associated with human leukocyte antigen-DRw5, iritis, and antinuclear antibody

Evidence has been sought for a genetically determined predisposition among children with juvenile rheumatoid arthritis (JRA) who are also at particular risk for the development of inflammatory eye disease.45 unrelated Caucasian patients (41 female) with early-onset pauciarticular JRA were human leukocyte antigen (HLA) types. 28 of the study group were found to be HLA-DRw5 compared with 16 of 84 controls (X(2), 24.3, P = <0.001). 9 patients were HLA-DRw8 compared with 4 of 84 controls (X(2), 7.51, P = <0.01). Iritis developed in 24 of the 45 children studied, 17 of whom were typed as HLA-DRw5 when compared to controls (X(2), 26.76, P = <0.001) and 6 with iritis typed as HLA-DRw8 (X(2), 9.10, P = <0.01). Antinuclear antibody was found in the serum of 17 of the 28 patients typing as HLA-DRw5 compared with 4 of the 17 who did not have this antigen (X(2), 5.88, P = <0.02). No such association was seen in patients with HLA-DRw8. In a study of linked genes, a delta value of 0.090 was found for HLA-DRw5 with HLA-B12, of 0.070 for DRw5 with HLA-Cw4, and a value of 0.050 for DRw5 and HLA-Bw35. This suggests a linkage disequilibrium between HLA-DRw5 and these two B series alleles, a conclusion which was supported by haplotype analysis in families of 11 of the disease probands. HLA-DRw5 has not previously been reported to be increased in any rheumatic disease group. It is proposed that HLA-DRw5 is a genetic marker defining those at risk for early-onset pauciarticular JRA with iritis.