An attenuated vaccine for AIDS?

Therapy for acute rejection in pediatric organ transplant recipients

Despite the availability of potent immunosuppressive drugs, rejection after organ transplantation in children remains a serious concern, and may lead to significant morbidity, graft loss, and death of the patient. Acute graft rejection in pediatric recipients is first treated with methylprednisolone pulses, followed by progressive taper of corticosteroid doses. After control of the rejection episode, baseline immunosuppression has to be adjusted and closely monitored since rejection (especially late episodes, occurring more than 6 months after transplantation) may be due to a lack of compliance or sub-therapeutic drug concentrations. The management of corticosteroid resistant rejection is not standardized, and depends on the transplanted organ and previous immunosuppressive regimen. In patients experiencing corticosteroid resistant acute rejection while on a cyclosporine-based immunosuppressive regimen, cyclosporine is generally changed to tacrolimus. In case of tacrolimus-based immunosuppression, tacrolimus blood levels may be increased, and/or mycophenolate mofetil (which nowadays tends to replace azathioprine) or sirolimus may be added, although pharmacodynamic data and clinical studies with these agents are still scarce in pediatric recipients. The use of antithymocyte globulins or monoclonal anti-CD3 antibodies, muromonab CD3 (OKT3) is hampered by numerous adverse effects, including a significant risk of over-immunosuppression. These therapies are nowadays indicated in very selected cases. Other treatments such as plasmapheresis and high dose immunoglobulins may be useful in difficult cases. In patients with refractory rejection despite therapeutic escalation, the risks of over-immunosuppression, including opportunistic infections and malignancies (especially the Epstein-Barr virus related post-transplant lymphoproliferative disease) have to be balanced with the consequences of graft loss due to rejection. Detransplantation or retransplantation may, in some instances, be preferable to severe infectious or tumoral complications.

Immunosuppression in elderly renal transplant recipients: are current regimens too aggressive?

Renal transplantation is an accepted and successful treatment modality in elderly patients with end-stage renal disease. In comparison with maintenance dialysis, transplantation has been shown to confer a mortality benefit as well as improvements in quality of life in older individuals with end-stage renal disease. Despite this, overall outcomes of renal transplantation in elderly individuals have, in general, been less successful than those of younger renal transplant recipients. Largely, this has been due to the particular vulnerability of elderly patients to the immunosuppressive medications used in renal transplantation. This review article covers these issues in some detail and briefly discusses some of the pharmacokinetic, pharmacodynamic, physiological and immunological differences between younger and older transplant recipients. Elderly renal transplant recipients have both a higher rate of patient death and allograft loss censored for death. Upon multivariate analysis, age of the recipient is strongly associated with allograft loss independent of other known factors. Acute rejections are less frequent in older individuals; however the consequence of a rejection if it occurs is negative for long-term graft survival. On the other hand, death by infection is vastly increased in older versus younger renal transplant recipients. In general, the pharmacokinetics of the immunosuppressive agents are little affected by age, but the tolerance to these agents seems to decrease with increasing age. Elderly renal transplant recipients present a very difficult clinical challenge. As the elderly become an ever-increasing segment of the renal transplant population, new and innovative immunosuppressive strategies will have to be considered and applied.

Live attenuated SIV vaccines are not effective in a postexposure vaccination model

Live attenuated simian immunodeficiency virus (SIV) vaccines, like nef deletion mutants, have been the most effective vaccines tested in the SIV/macaque model so far. The efficacy of live attenuated SIV vaccines in therapeutic vaccination and postexposure prophylaxis has not been determined. Inoculation of macaques with a pathogenic challenge virus and an attenuated SIV vaccine at the same time mimics postexposure vaccination, whereby vaccination with the attenuated virus is performed as rapidly as possible after exposure to pathogenic SIV. In the study presented here, four rhesus macaques were coinfected with pathogenic SIV and a nearly 3000-fold excess of a nef deletion mutant of SIV. Four macaques received pathogenic SIV and an approximately 200-fold excess of a nef deletion mutant expressing interleukin 2 (IL-2). The IL-2-expressing SIV had been previously constructed to enhance the immunogenicity of live attenuated SIV vaccines. All coinfected macaques had a high viral load, and some of them developed AIDS-like symptoms and pathological alterations rapidly. In the presence of pathogenic SIV, both live attenuated SIV vaccines did not protect from disease in this postexposure vaccination model.