Efficient Expansion of Human Granzyme B-Expressing B Cells with Potent Regulatory Properties.

Granzyme B-expressing B cells have been shown to be an important regulatory B cell subset in humans. However, it is unclear which subpopulations of B cells express GZMB under normal conditions and which protocols effectively induce ex vivo expansion of GZMB+ B cells. We found that in the peripheral blood of normal individuals, plasmablasts were the major B cell subpopulation that expressed GZMB. However, when using an in vitro plasmablast differentiation protocol, we obtained only 2% GZMB+ B cells. Nevertheless, using an expansion mixture containing IL-21, anti-BCR, CpG oligodeoxynucleotide, CD40L, and IL-2, we were able to obtain more than 90% GZMB+ B cells after 3 d culture. GZMB+ B cells obtained through this protocol suppressed the proliferation of autologous and allogenic CD4+CD25- effector T cells. The suppressive effect of GZMB+ B cells was partially GZMB dependent and totally contact dependent but was not associated with an increase in effector T cell apoptosis or uptake of GZMB by effector T cells. Interestingly, we showed that GZMB produced by B cells promoted GZMB+ B cell proliferation in ERK1/2-dependent manner, facilitating GZMB+ B cell expansion. However, GZMB+ B cells tended to undergo apoptosis after prolonged stimulation, which may be considered a negative feedback mechanism to limit their uncontrolled expansion. Finally, we found that expanded GZMB+ B cells exhibited a regulatory phenotype and were enriched in CD307bhi, CD258hiCD72hi, and CD21loPD-1hi B cell subpopulations. Our study, to our knowledge, provides new insight into biology of GZMB+ B cells and an efficient method to expand GZMB+ B cells for future cell therapy applications.

Rituximab as induction therapy in pediatric kidney transplantation: A single-center experience in four patients.

BACKGROUND: The anti-CD20 rituximab is often used in the treatment of children with steroid-resistant nephrotic syndrome or EBV-induced post-transplant lymphoproliferative disorder. This single-center series reports the use of rituximab as induction therapy in pediatric kidney transplantation. METHODS: Four children who received rituximab as induction therapy for kidney transplantation since 2016 were retrospectively analyzed. Clinical and laboratory data were extracted from medical records. RESULTS: The patients (2 boys and 2 girls) were aged from 6.1 to 11.9 years and were treated with rituximab on the day of the transplantation procedure; all the transplants came from deceased donors. In all patients, rituximab was used because of positive EBV viral loads before kidney transplantation. Viral loads remained undetectable for the first 6 months after the transplantation procedure and remained below the 4.5 log threshold thereafter. After a median follow-up of 2.3 years, none of the patients displayed rejection or de novo donor-specific antibodies; the glomerular filtration rate remained above 70 ml/min/1.73 m2 . No post-transplant lymphoproliferative disorder was observed. CONCLUSION: The results suggest that rituximab can be used as induction therapy to prevent EBV replication and its complications in case of positive viral load prior to kidney transplantation.

Ofatumumab treatment for nephrotic syndrome recurrence after pediatric renal transplantation.

BACKGROUND: Relapsing nephrotic syndrome (NS) after transplantation can be a challenge to treat. The result of the consequent long-lasting proteinuria is the loss of the graft. Disease recurrence after renal transplantation occurs in around half of cases, and the efficacy of therapeutic strategies is often limited. Recently, ofatumumab, a second-generation and fully human anti-CD20 monoclonal antibody, has been shown to be effective in severe situations. METHODS: We retrospectively collected data from the medical records of children with recurrence of NS after renal transplantation treated with ofatumumab in France, after failure of previous treatments. RESULTS: Six patients were included in this study in five centers with a median duration of follow-up of 10.5 months. Two different ofatumumab regimens were administered. The primary outcome was proteinuria at 6 months after the last dose of ofatumumab. No patient achieved a complete remission, 3/6 had a partial remission, and 3/6 had no response to ofatumumab. Four patients exhibited a minor allergic reaction with the first infusion. One patient died of infection, as a consequence of multiple factors. No malignancies were observed; however, the time of follow-up was not sufficient to see such disease. CONCLUSIONS: Altogether, these results suggest ofatumumab has a poor efficacy in treating recurrence of NS after renal transplantation. However, it could be discussed in multidrug-resistant refractory NS, but infectious complications and overimmunosuppression have to be balanced. There is a need for further studies to confirm these findings and safety and to determine a standardized protocol in this indication.

Ofatumumab in post-transplantation recurrence of a pediatric steroid-resistant idiopathic nephrotic syndrome.

Treatment of SRNS is a challenge. Antiproliferative agents and depleting antibodies have been reported to be effective. However, these agents are not always successful, and use of ofatumumab could provide a different treatment option. Our patient was diagnosed with a SRNS at 5 years of age. She developed ESRD, with FSGS. This was cause for a first renal transplantation. The NS relapsed, leading to loss of the graft, and a second renal transplantation was performed. Due to the recurrence of the NS, IAds were initiated and led to a complete remission. Our patient remained dependent on IAds, however, despite treatments with calcineurin inhibitors, corticosteroids, rituximab, and abatacept. Ofatumumab was introduced and led to a remission, thus allowing cessation of the IAd treatment. Another infusion of ofatumumab was administered 8 months after the last one, due to the recurrence of the NS and a renewed increase in B cells. Although it did not result in a complete remission, the proteinuria was stabilized in the absence of IAds. Ofatumumab may be an alternative treatment for post-transplantation rituximab-resistant SRNS, although this needs to be confirmed by further studies.