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Studies were performed to determine in vitro and in vivo effects of acetylation on Fab' fragments of ZCE-025, a monoclonal anti-CEA antibody. Isoelectric focusing revealed a drop in isoelectric point of 1.7 pI units following acetylation. Biodistribution studies of acetylated and nonacetylated [111In]Fab' were performed in normal BALB/c mice and in nude mice bearing the T-380 CEA-producing human colon tumor. The acetylated fragments remained in the vascular compartment longer and had significantly diminished renal uptake of 111In compared to controls. While acetylation itself effected a 50% drop in immunoreactivity, tumor uptake of the acetylated and nonacetylated 111In-labeled Fab' fragments was comparable, with the exception of one data point, through 72 h.

Toxicity was assessed during and following 186 infusions of various murine monoclonal antibodies (MoAbs) in 82 patients afflicted with 10 different malignancies. Doses ranged from 0.5 to 500 mg per infusion and were administered over 0.25-24 h. Reactions of varying degrees were noted in 27 patients (33%) during or following 57 (31%) infusions. For antibodies that reacted with circulating cells, toxicity was seen in 20/82 of the first infusions compared with 0/55 for patients receiving antibodies that did not react with circulating cells. A 25% decrease in white blood cells (WBC) was associated with side effects in 40/66 courses whereas only 9/81 courses were associated with any sort of toxicity when the WBC decreased by less than 25%. Fevers, rigors, chills, and diaphoresis were observed in 21-23% of patients, but only in association with removal of circulating cells that bound the antibody. Presumed hypersensitivity reactions, including urticaria, pruritus, bronchospasm, and anaphylaxis occurred in 15 patients (18%). The two episodes of bronchospasm and single episode of anaphylaxis occurred in patients treated more than once, at least 2 weeks after a previous treatment. There was no clear relationship between dose or rate of infusion and toxicity for these antibodies. We conclude that murine MoAbs can be given with an acceptable frequency of serious allergic reactions and that the biologic effects of specific antibody-antigen reactions may be a more significant source of toxicity for such antibodies.

It is the opinion of the authors that the molecule of the future for radioimmunodetection (and hopefully radioimmunotherapy and delivery of drugs) will have the following characteristics: It will be an altered fragment, rather than an intact molecule or fragment. It will be small, perhaps 60,000 molecular weight, yet remain in the vascular compartment for a comparatively long period of time, then be eliminated via the kidney. It will be of human origin or a murine molecule altered to mask its immunogenic properties. It will be 111In- or 99mTc-labeled or bifunctionally chelated to another metal ion. It will target a cell surface antigen, but one that does not circulate. It will be used in combination with derivatives of other MoAbs that target other antigens on the cell. It would be a hapten-type device that follows the administration of a "bifunctional MoAb." Whatever the final molecule, it will be administered to a patient who has been "prepped" with an antigen-enhancing substance or one that "unmasks" a gene and allows a repressed marker to be expressed by the tumor cell to which the MoAb was developed. It may be a MoAb that attaches to a white cell, which then chemotactically seeks the tumor that has been previously induced to produce a substance that the white cell recognizes.

We report results of 24-h continuous infusions of murine monoclonal antibody T101 in six patients with chronic lymphocytic leukemia (CLL), and 10 with cutaneous T-cell lymphoma (CTCL), at doses of 10, 50, 100, or 500 mg. Similar side-effects were seen in CLL and CTCL, including direct toxic effects of therapy, such as fever, sweats, and chilling, and a 30% frequency of allergic manifestations. In vivo binding of T101 to target cells in blood, skin, lymph nodes, tumor masses, and bone marrow was demonstrated. Antigenic modulation occurred rapidly in all cases, and persisted throughout the infusion period. Peak serum T101 levels for equivalent doses were somewhat higher, and persisted longer in CTCL, perhaps because of differences in the number of circulating target cells. Antimouse antibodies were demonstrated in 5 of 10 CTCL vs. 0 of 6 CLL patients. In all five cases, there was a substantial component of T101 specificity in the antimouse response. Brief objective clinical responses were observed in 4 of 10 CTCL and 2 of 6 CLL patients. Acute anti-tumor effects of T101 were substantially more dramatic in CTCL than CLL, but appeared limited by antigenic modulation and the emergence of antimouse antibodies. In view of the in vivo binding and modulation, more durable anti-tumor effects may be achievable with cytotoxic immunoconjugates of this monoclonal antibody.