Radiolabeled antibody targeting of the HER-2/neu oncoprotein.

The HER-2/neu oncogene encodes a Mr 185,000 transmembrane phosphoglycoprotein which is overexpressed in 25-35% of breast and ovarian neoplasms and portends a poor prognosis. We have studied the feasibility of targeting this oncoprotein, designated p185, with radioiodinated murine monoclonal antibodies (muMABs) 4D5 and 7C2, which recognize distinct epitopes on its extracellular domain. The rates of internalization and catabolism of these antibodies were analyzed by cellular radioimmunoassay and electron microscopy. After binding to NIH3T3 HER-2/neu cells, which show high surface expression of p185, the muMABs were endocytosed via coated pits, routed to lysosomes, and degraded. Approximately 44% of 125I-4D5 and 39% of 125I-7C2 were catabolized by tumor cells after 24 h. The biodistribution of radiolabeled 4D5 and 7C2 were evaluated in beige/nude mice bearing s.c. NIH3T3 HER-2/neu grafts. A high specificity of localization was seen with tumor:organ ratios of activity generally ranging from 5:1 to 30:1. However, the percentage injected dose of radioactivity per gram of tumor declined sharply from 25% at 24 h to 5% at 120 h postinjection. Treating the animals with 400-700 muCi 131I-4D5 caused a marked inhibition of tumor growth, although no mice were cured. Unlabeled 4D5 had no effect on tumor progression in this model, but administering 400-700 muCi of 131I-DA4-4, an isotype-matched irrelevant muMAB, resulted in an intermediate degree of growth retardation. Analysis of kinetic blood data and whole-body time-activity curves indicated that the irrelevant conjugate remained in the body 2-3 times longer than 131I-4D5. Radioiodinated anti-HER-2/neu muMABs are attractive agents for radioimmunodiagnosis and radioimmunotherapy of aggressive HER-2/neu-positive breast and ovarian carcinomas, but effective strategies for retarding intratumoral catabolism may be necessary to optimize their clinical utility.

Haploidentical bone marrow transplants for two patients with reticular dysgenesis.

We report two cases of reticular dysgenesis (RD) successfully treated by BMT utilizing T cell-depleted haploidentical marrow grafts. One child failed to engraft after conditioning with ATG, and the other failed two transplant attempts with cyclophosphamide + ATG, and busulfan + cyclophosphamide + ATG, respectively. Donor engraftment was achieved in both patients following treatment with 700 cGy TBI, with or without other agents. These results, taken together with previous reports in the literature, suggest that children with RD may require more intensive conditioning than patients with other types of severe combined immunodeficiency syndrome.

Maternal mosaicism for a novel interleukin-2 receptor gamma-chain mutation causing X-linked severe combined immunodeficiency in a Navajo kindred.

X-linked severe combined immunodeficiency disease (SCID) results from mutations of IL2RG, the gene encoding the interleukin-2 receptor gamma chain, also known as the common gamma chain (gamma c). A distinct form of autosomal recessive SCID occurs at an increased frequency among the Navajo Native American population. The disease gene responsible for autosomal Navajo SCID remains to be determined. We report the occurrence of X-linked SCID in a Navajo Native American kindred with two affected brothers. X-linked SCID was suggested by the presence of circulating B cells and the absence of surface gamma c expression in a cell line derived from an affected male. A C-to-T transition was demonstrated in exon 5 of the IL2RG gene, resulting in the substitution of tryptophan for arginine at position 224. This change was not present in the peripheral blood lymphocytes of the mother, thus proving the occurrence of a new mutation in the maternal germline. This report underscores the importance of establishing a specific genetic diagnosis for SCID cases and illustrates the inherent difficulties in providing genetic counseling in cases involving mosaicism.

Langerhans cell deficiency in reticular dysgenesis.

Reticular dysgenesis is a rare inherited immunodeficiency characterized by the lack of blood monocytes and neutrophils and low lymphocyte counts, contrasting with normal red blood cell counts and normal or decreased platelet counts. Whether dendritic cells or macrophages, both of which derive primarily from blood monocytes, are affected in this condition remains unknown. We studied 7 patients with reticular dysgenesis. Macrophages were present in normal numbers in the dermis and in the atrophic lymphoid tissues of these patients, proving that at least some subsets of macrophages can differentiate despite very low monocyte counts. By contrast, Langerhans cells, which are CD1a-positive epidermal dendritic cells, were absent in all (n = 5) patients before bone marrow transplantation. After bone marrow transplantation, Langerhans cells were present (n = 2), suggesting that the defect is not related to keratinocyte dysfunction. A split chimeric reconstitution, characterized by the presence of autologous blood monocytes able to differentiate in vitro into CD1a-positive dendritic cells, was observed in a patient who underwent successful engraftment. These results suggest that an intrinsic cell defect is unlikely and that a bone marrow-derived factor may be defective in reticular dysgenesis; it may be responsible for the Langerhans cell defect but not involved in macrophage differentiation.