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Antibodies raised in rabbits against a mouse plasma cell tumor were labeled with 131 I and injected along with normal rabbit globulin labeled with 125 I into plasmacytoma bearing mice and the degree of localization of the antibodies in the tumors determined. There was localization of the anti-tumor antibody above the background localization of the normal globulins. The localization apparently took place largely on the tumor cell surfaces since following cell fractionation experiments the fixation was found to be largely in the microsome fraction. The antibodies raised against the tumor also showed localization in liver, spleen and brain.

Different mouse plasma cell tumors have been shown to produce different homogenous species of myeloma immunoglobulin in large amounts and are currently thought to consist of monoclonal cells ( Potter et al. , 1965 ; Lennox and Cohn, 1967 ). We have previously observed multiple isoaccepting tRNA's in a tumor of this type, MOPC 31C ( Yang and Novelli, 1968a ). In the present work, comparative studies of isoaccepting tRNA's by co-chromatography on a reversed-phase chromatographic column have been performed on cell lines of transplantable mouse plasma cell tumors that produce different kinds of myeloma immunoglobulin. Similar chromatographic patterns were observed for most of the aminoacyl-tRNA's examined in these tumors. A marked difference, however, was found between the seryl-tRNA's of an immunoglobulin-A producer (MPC 62) and those of immunoglobulin-G producers (MPC 47 and MOPC 31C).

The effects of cis-dichlorodiammineplatinum(II) on experimental tumours and its preliminary trials in man has led to the search for related compounds with anti-tumour activity. A number of platinum complexes have been prepared and tested for their ability to cause regression of a mouse plasma cell tumour. A class of compounds have been found which are some thirty to forty times more active against the plasma cell tumour than the platinum complex at present on clinical trial.

SummaryExperimental mouse plasma cell tumor, X5563, produces plasma gamma globulin alterations. Temporary disappearance of abnormal globulin occurs following partial removal of neoplasm. Homologous transplantation of tumor has been carried out. Because surviving tumor can be readily identified by changes in plasma proteins without animal sacrifice, it provides a new and useful tool for investigation of tumor immunity.

WE have already investigated the production of immunoglobulin G (IgG) by mouse plasma cell tumour 5563 and have shown that light chains are released autonomously from polyribosomes into a pool of free light chains. The time course of incorporation of radioactive amino-acids into free light chain and the myeloma protein indicated that the pool of free light chains is small and reaches maximum radioactivity after about 10 min of incubation. It behaves as a pool with rapid turnover from which light chains appear to be incorporated into G myeloma protein molecules1,2. These findings led us to propose the possibility that the pool of free light chains controls the release of heavy chains from the polyribosomes.

It is well recognized that immunoglobulins consist of heterogeneous populations of antibody proteins which are synthesized following a complicated series of cellular events induced by antigen stimulation. Chemical studies of purified antibodies suggested that antibodies of different specificities may differ from one another in their primary protein structure (Koshland and Englberger, 1963). The mechanism by which this tremendous variety of immunoglobulins are synthesized has thus been a very interesting biological problem. Biochemical knowledge concerning transcription and translation of the genetic messages for the synthesis of these proteins is, however, extremely deficient. This is due mainly to the difficulty in obtaining for study a sufficient quantity of lymphoid tissue with a given homogeneity of antibody production.

A protein (denoted L′) which is similar in structure to immunoglobulin light chain has been isolated from the mouse plasma cell tumor, RPC-20. L′ has a molecular weight which is about 6000 daltons less than light chain. The exact nature of the relationship between L′ and light chain has not been established.

THE plasma cell tumour designated X5563 originated in a 22½-month-old female C3H/He mouse in the Cancer Research Genetics Laboratory, Berkeley, California. It was successfully transplanted by Dr. H. I. Pilgrim, and mice bearing the second transplant generation were sent to the National Cancer Institute, Bethesda, Maryland, where it was routinely transplanted every 60 days in C3H/He mice for several transplant generations1,2. Mice inoculated with the tumour were sent to us by Dr. M. Potter, of the National Cancer Institute. The tumour is now in its third transplant generation in our hands.

The biology of large solid tumours regressing with nitrogen mustard treatment: a study of the mouse plasma cell tumour Adj-pc-5 and the Walker carcinosarcoma 256.

The origin of the myeloma protein found in mice bearing the plasma cell tumor X5563 has been investigated. Specific activity-time curves of the myeloma proteins isolated from the tumor and from the plasma of these animals were compared following intravenous injection of L-lysine-C14. The results indicate that myeloma protein is synthesized in the plasma cell tumor.