an immunotoxin is defined as any immunological molecule such as an antibody which has been conjugated with a toxin , preferably a cytotoxin . the present invention is directed to a method of treating an individual having a pathophysiological state , comprising the step of administering to said individual an a pharmacologically effective dose of an agent which upregulates the expression of a cellular target . this administration is followed by the administration of a pharmacologically effective dose of an immunotoxin directed against the cellular target . preferably , the administered agent is selected from the group consisting of differentiating agents , cytokines , interleukin - 2 , tumor necrosis factor , interferon - α , interferon - γ and peptide hormones . in one embodiment , the invention comprises the administration of a pharmacologically effective dose of a retinoid . preferably , the retinoid induces expression of cd38 antigen in cells . if this is the case , a pharmacologically effective dose of a anti - cd38 immunotoxin is administered . representative pathophysiological states which may be treated using the methods of this embodiment of the invention include rarα selective acute myeloid leukemia , acute promyelocytic leukemia , lymphomas , and myelomas . representative retinoic acid metabolites which may be used in the methods of the present invention include all - trans - retinoic acid ( ra ); 9 - cis retinoic acid ( 9 - cis ra ); ( e )- 4 -[ 2 -( 5 , 6 , 7 , 8 - tetrahydro - 5 , 5 , 8 , 8 - tetramethyl - 2 - naphthalenyl )- 1 - propenyl ] benzoic acid ( ttnpb ); ( e )- 4 -[ 2 -( 5 , 6 , 7 , 8 - tetrahydro - 3 , 5 , 5 , 8 , 8 - pentamethyl - 2 - naphthalenyl )- 1 - propenyl ] benzoic acid ( 3 - met ttnpb ); and other retinoids that can bind and activate the rarα receptor . preferably , the retinoid is administered in a dose of from about 0 . 1 mg / kg to about 2 mg / kg . the immunotoxin used in the methods of the present invention specifically target cells expressing the cd38 antigen . preferably , the immunotoxin comprises a monoclonal antibody directed against the cd38 antigen conjugated to a toxin molecule . although a person having ordinary skill in this art could substitute any toxin , a preferred toxin useful in these methods is gelonin . although a person having ordinary skill in this art could substitute any monoclonal antibody specific for the cd38 antigen , ib4 or ib6 antibodies were used herein to demonstrate the present methods . preferably , the immunotoxin is administered in a dose of from about 0 . 05 mg / kg to about 2 mg / kg . the following examples are given for the purpose of illustrating various embodiments of the invention and are not meant to limit the present invention in any fashion . cd38 expression in normal tissues is limited mainly to the thymus . the tissue specificity of cd38 was examined by the hybridization of a radiolabeled cd38 nucleic acid probe against a commercial ( clontech ) tissue specific mrna dot blot . the results of the hybridization are shown in fig1 . it was observed that cd38 is mainly expressed in the thymus with significantly lower levels of expression in the prostate . retinoic acid ( ra ) augments the cytotoxic effect of immunotoxin through enhanced expression of cd38 . hl - 60 cells were incubated with either immunotoxin alone or in the presence of 5 nm retinoic acid ( ra ). increasing concentrations of unconjugated ib4 monoclonal antibody were added to the cells incubated with immunotoxin and retinoic acid . after three days , the cells were assayed for viability with the mts assay . briefly , 6 . 5 mg / ml mts solution [( 3 -( 4 , 5 - dimethylthiazol - 2 - yl )- 5 -( 3 - carboxymethoxyphenyl )- 2 -( 4 - sulfophenyl )- 2h - tetrazolium ] and 0 . 5 mm pms ( phenazine methosulfate ) solution were mixed at a ratio of 20 : 1 . 20 μl of the combined mts / pms solution was placed in each well of a 96 well plate containing samples of the cells to be tested . the plate was incubated for 1 – 4 hours at 37 ° c . in a 5 % co 2 atmosphere , after which time , the amount of formazan produced by live cells from cellular reduction of mts was measured by reading the absorbance at 490 nm . the results are shown in fig2 . immunotoxin alone had little effect on the viability of the cells ( c ). however , when the cells were incubated with immunotoxin in the presence of 5 nm retinoic acid , a significant reduction in cell viability was observed . increasing concentrations of unconjugated ib4 monoclonal antibody blocked the cytotoxic effect of immunotoxin and retinoic acid . the fact that unconjugated ib4 blocked the ability of the immunotoxin to kill the cells demonstrates that the immunotoxin is specifically interacting with the cd38 surface marker and that the effect of the retinoic acid is to increase the expression of the cd38 antigen . all - trans - retinoic acid ( ra ) pretreatment enhances the induced killing of hl - 60 cells . hl - 60 cells were preincubated overnight in either the presence or absence of 5 nm all - trans - retinoic acid . the cells were washed twice and incubated in increasing concentrations of immunotoxin in either the presence or absence of ib4 unconjugated anti - cd38 moab . after three days , the cell were assayed for viability . the results are shown in fig3 . preincubation with all - trans - retinoic acid followed by immunotoxin treatment resulted in more cell death than treatment with immunotoxin alone . the presence of 100 fold excess of the unconjugated anti - cd38 monoclonal antibody ib4 blocked the toxicity of the immunotoxin in both cases by competing with the immunotoxin for access to the cd38 markers on the cells . these results demonstrate that the all - trans - retinoic acid ( ra ) was causing some change in the cells which render them more susceptible to the immunotoxin rather than playing a direct role in the death of the target cells . gelonin must be conjugated to the anti - cd38 antibody to have a toxic effect on the target cells . hl - 60 cells were incubated for three days with increasing concentrations of either immunotoxin or gelonin in either the presence or absence of 5 nm retinoic acid . afterwards , the cells were assayed for viability using the mts assay . as seen in fig4 , gelonin alone had no toxic effect in either the presence of absence of 5 nm . thus , the toxic effect of gelonin depends on it being conjugated to the anti - cd38 monoclonal antibody in order to deliver the toxin to the cell . even nominal levels of all - trans - retinoic acid ( ra ) lead to increased toxicity of the immunotoxin . hl - 60 were incubated with either immunotoxin or unconjugated ib4 monoclonal antibody in increasing concentrations of monoclonal antibody . fig5 shows that even the lowest level of all - trans - retinoic acid ( ra ) ( 1 nm ) lead to almost complete killing of the target cells by the immunotoxin . this effect was not observed with the unconjugated monoclonal antibody . this result indicates that it is the gelonin conjugated to the monoclonal antibody in the immunotoxin that leads to the increased cell death rather than some effect of the antibody itself . retinoic acid can induce expression of the cd38 marker in a variety of cell lines . the daudi , thp - 1 , k562 , and hl60 - rarα cell lines were treated with increasing concentrations of immunotoxin in either the presence or absence of 5 nm all - trans - retinoic acid ( ra ). after three days , the viability of the cells was examined using the mts assay , which is shown in fig6 . in the thp - 1 and hl60 - rarα cell lines , all - trans - retinoic acid induced cell death while the cell which were cultured in the absence of all - trans - retinoic acid were mostly unaffected by the immunotoxin . in the daudi cells , which have a high basal expression of cd38 , the immunotoxin resulted in almost complete cell death regardless of whether retinoic acid was present . on the other hand , k562 , which are resistant to ra - induced cd38 expression , were unaffected by the immunotoxin regardless of the presence of retinoic acid . hl - 60 subcloned cells , resistant to adriamycin - induced killing were cultured with immunotoxin either alone or in the presence of 5 nm all - trans - retinoic acid . after three days , the mts assay was used to test cell viability . fig7 shows the results obtained . some cell death was observed in the presence of immunotoxin alone which was greatly augmented by the addition of 5 nm all - trans - retinoic acid . cells which have high basal expression of cd38 are killed by immunotoxin regardless of the presence or absence of all - trans - retinoic acid ( ra ). mz , a non - hodgkin lymphoma cell line which has a high basal expression of cd38 , was treated with increasing amounts of immunotoxin in either the presence or absence of 5 nm all - trans - retinoic acid . the addition of immunotoxin resulted in a high level of cell death regardless of the presence or absence of retinoic acid ( fig8 ). this is strong evidence that retinoic acid is increasing the toxicity of immunotoxin by enhancing the level of cd38 on other cell lines which do not have a high basal level of cd38 . retinoic increases cd38 expression in a number of lymphoid tumor cells . table i lists the potential targets for anti - cd38 bound toxin treatment a number of different lymphoid tumor cell lines were treated with 5 nm all - trans - retinoic acid ( ra ). afterwards , the expression of cd38 in untreated versus treated cell was measured by flow cytometry . a significant rise in cd38 expression was observed in acute myeloid leukemia ( aml ), acute promyelocytic leukemia ( apl ), lymphoma , and myeloma tumor cells . the increase in cd38 expression ranges from 2 . 5 to 20 fold . thus , retinoic acid can be used in all of these tumor types to increase the vulnerability of the tumor cells to immunotoxin treatment . hl - 60 cells with a mutated rarα gene that renders the cells resistant to the effects of retinoic acid were treated with immunotoxin in either the presence or absence of 5 nm retinoic acid . in these cells , the addition of retinoic acid had no effect on the toxicity of the immunotoxin . as shown in fig9 , no appreciable cell death was observed in the cells treated with all - trans - retinoic acid ( ra ), with unconjugated ib4 and gelonin , or with gelonin alone . this is further proof that the immunotoxin kills cells which are affected by retinoic acid because of a retinoid induced increased in expression of cd38 target of the immunotoxin . any patents or publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains . these patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference . one skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned , as well as those inherent therein . the present examples along with the methods , procedures , treatments , molecules , and specific compounds described herein are presently representative of preferred embodiments , are exemplary , and are not intended as limitations on the scope of the invention . changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention as defined by the scope of the claims .
the present invention is directed to the use of agents that induce high levels of cell surface molecules to provide targets for immunotoxins directed against the same cell surface molecules . a specific example is given in which all - trans - retinoic acid is used to induce high levels of cd38 cell surface antigen expression in several myeloid and lymphoid leukemia cells . cd38 was then used as target for delivering plant toxin to leukemia cells . treatment of leukemia cells with ra induced high levels of cd38 in those cells that otherwise had low cd38 expression . the ra - induced leukemia cells then became exquisitely sensitive to an immunotoxin constructed from an anti - cd38 monoclonal antibody conjugated to the plant toxin gelonin .