RTX can be safely administered and may be an effective agent to reduce high-titer anti-HLA Abs in subjects awaiting kidney transplantation.

correspondence n engl j med 354;18 www.nejm.org may 4, 2006 1961fears. As Dr. Lear states, many beneficiaries (and their providers) are worried, frustrated, and scared. We hope that our guarded optimism will one day seem more prescient than do such fears. At the moment, it appears that patients, doctors, and pharmacists are struggling with information overload and a panoply of poorly understood options.

No abstract

The response to primary immunization in patients treated with Rituximab (RIT) is not clear. We studied the in vivo antibody response of chronic renal failure (CRF) patients to the neoantigen bacteriophage phiX174 given alone or after ablation with RIT. Eighteen CRF subjects received two immunizations with phiX174 separated by 6 weeks. Nine subjects received a single dose of RIT. The intensity and immunoglobulin isotype of the antibody response (K v ) were measured post-infusion. In addition, three subjects previously immunized and treated with RIT underwent a third and fourth immunization with phiX174 and a tetanus control 2 years later. RIT significantly decreased peak K v responses when compared to both historic non-CRF controls and to CRF subjects. CRF itself decreased peak K v responses compared to non-CRF controls. Percent-ratio of anti-phage IgM to IgG was significantly decreased in RIT treated subjects. One of three subjects treated with RIT was found to have developed a partial B cell tolerance to phiX174 administration 2 years later. RIT decreases antibody production and isotype switching to neoantigens and might be useful to prevent antibody response to therapeutic drugs and to newly transplanted organs.

Pre-formed HLA antibodies (Ab), reported as panel-reactive antibody (PRA), prolong transplant waiting time. We hypothesized that rituximab (RIT) could reduce PRA via B-cell depletion. As part of a Phase I study of single RIT dose, we studied in vivo and ex vivo effects on T-cell immune responses. Nine subjects (n = 3) were treated at 50, 150, and 375 mg/m(2). Serum interleukin-1alpha (IL-1alpha), IL-6, IL-12, tumor necrosis factor beta (TNF-beta), and interferon-gamma (IFN-gamma) were measured by enzyme-linked immunosorbent assay (ELISA). T-cell function was monitored with T-cell proliferation assays. IL-6 levels rose in eight patients (7.15 +/- 4.38 pg/mL to 86.22 +/- 77.08, p = 0.021). The high-dose group had detectable TNF-betapost rituximab infusion (874.7 +/- 1466.5 pg/mL). There was no decline in T-cell proliferation in response to phytohemagglutinin or allogeneic lymphocyte stimuli. Stimulation indices in the presence of both concentrations of tetanus toxoid rose significantly at 4 weeks.

Pharmacokinetic sampling was performed in two multicenter trials in which basiliximab (anti-CD25 monoclonal antibody) was administered with triple immunosuppression consisting of cyclosporine microemulsion, corticosteroids, and either azathioprine or mycophenolate mofetil. Blood samples were collected over 12 wk post-transplant from 31 azathioprine-treated and 66 mycophenolate mofetil-treated patients. Empirical Bayes estimates of each patient's basiliximab disposition parameters were derived and the duration of CD25 saturation was estimated as the time over which serum concentrations exceeded 0.2 microg/mL as confirmed by flow cytometry measurements. Basiliximab clearance was 29+/-14 mL/h when coadministered with azathioprine and 18+/-8 mL/h with mycophenolate mofetil. Both were significantly lower compared with a clearance of 37+/-15 mL/h from a previous study of basiliximab with dual therapy (p<0.001). As a consequence of the lower clearance of basiliximab, the durations of CD25 saturation were prolonged in the presence of azathioprine (50+/-20 d; range, 13--84) and mycophenolate mofetil (59+/-17 d; range, 28--94) compared with dual therapy (36+/-14 d; range, 12--91). A total of 27 acute rejection episodes occurred during the first 6 months in the two studies. Durations of CD25 saturation were not different in these patients compared with those who remained rejection-free in each study. A single patient among 57 who were screened developed anti-idiotype antibodies to basiliximab. The average duration of CD25 saturation was prolonged by 39 and 64% in the presence of azathioprine and mycophenolate mofetil, respectively. This graded effect was also observed for basiliximab clearance and may be due in part to a differentially reduced humoral response to basiliximab. Nonetheless, the range of CD25 saturation durations and basiliximab clearances did not extend outside the range when basiliximab was used with dual therapy in the absence of these agents. Hence, no dosing adjustment is deemed necessary when basiliximab is used in triple immunosuppressive therapy including either azathioprine or mycophenolate mofetil.

False-positive Histoplasma antigen results were identified in two patients who received rabbit antithymocyte globulin (ATG, Thymoglobulin(R)) to prevent allograft rejection. To determine the prevalence of false-positive results following the administration of Thymoglobulin, sequential specimens were tested from a cohort of transplant recipients. Of 107 such patients, 17 (15.9%) demonstrated false-positive tests for Histoplasma antigenemia. False antigenemia peaked at 2-4 weeks after ATG administration and cleared over the next few months. Physicians should be aware of the potential for false-positive results in specimens from patients who have received ATG.

No abstract