Hybrid membrane IgM with the transmembrane region of I-A alpha facilitates enhanced presentation of distinct epitopes to T cells.

The role of B cell Ag receptors (membrane Ig or mIg) in the efficient Ag presentation to T cells, including the requirement of mIgM-associated Ig alpha/Igbeta, remains unclear. We report here that mIgM, substituted with greater than two-thirds of the NH2-terminal A alpha transmembrane (TM) regions of the MHC class II molecule, are capable of mediating the efficient presentation of specific Ag to some (Group 1) but not all (Group 2) T cell hybridomas. In contrast, the generation of epitopes recognized by the Group 2 hybridomas can be mediated only by the wild-type mIgM. Tyrosine phosphorylation appears to be necessary for the enhanced Ag presentation to Group 2 hybridomas, while it does not for Group 1 hybridomas. In addition, differential sensitivity of Ag processing to leupeptin, different duration required for epitope generation/presentation, as well as the involvement of distinct epitopes for stimulation of these groups of T cell hybridomas were observed. These results suggest that transport of the mIgM/Ag complexes to an endocytic compartment(s) for generation of certain T cell epitopes may be mediated by the N-terminal TM sequence of mIgM, independent of Ig alpha/Igbeta association. This function can be replaced by two-thirds of the NH2-terminal TM region of A alpha chain of class II molecules.

Phase II trial of ifosfamide with mesna in previously treated metastatic sarcoma.

Ifosfamide given to 42 patients iv at 2-2.5 g/m2/day X 4 resulted in partial responses in ten of 28 (36%) evaluable patients with adult soft tissue sarcomas, including two of two with chondrosarcoma; none of nine with pediatric sarcomas (Ewing's sarcoma, osteogenic sarcoma, or rhabdomyosarcoma) achieved partial response. All of the pediatric patients had failed to respond to complicated three- to six-drug regimens of up to 18 months in duration. The response rates in patients with and without prior cyclophosphamide (32%; seven responses among 22 patients; and 20%, three responses among 15 patients) were not significantly different, supporting in vitro evidence of a lack of cross-resistance between the two related compounds. Myelosuppression was dose-limiting. Hemorrhagic cystitis was not observed in patients treated with 400-500 mg of mesna iv every 4 hours during ifosfamide treatment. Nausea and vomiting were generally mild or moderate. Alopecia was universal but reversible. Of the first 11 patients, five became somnolent or developed visual hallucinations (during six of the 12 total courses administered to the five patients). Only one patient had two episodes of neurotoxicity. After reduction of the use of iv antiemetics and major narcotics, single episodes of neurotoxicity were seen in five of the next 27 patients. An asymptomatic acidosis developed in most patients, requiring bicarbonate replacement in one. Ifosfamide appears to be active in previously treated patients with sarcomas and should be evaluated in patients with less extensive prior treatment.