without thymic treatment , rhesus monkey renal allografts reject at a mean of 9 days . renal allografts in rhesus monkeys ( age 2 - 5 years ; 2 - 3 kg body weight ) were performed for the purpose of establishing a model of thymic tolerance in primates . the experimental protocol consisted of first selecting mhc class i disparate rhesus monkey donors and recipients . donor lymphocytes were injected into the recipient thymus gland 7 days prior to renal allografting from the same donor . recipients received the immunotoxin of the present invention by intravenous injection . renal allografts were performed and recipients underwent native nephrectomy . techniques for preparing anti - cd3 - crm9 ( where the antibody is directed at the human t - cell receptor complex &# 34 ; cd3 &# 34 ;) have previously been described . see u . s . pat . no . 5 , 167 , 956 and d . neville et al ., 89 p . n . a . s . usa 2585 - 2589 ( 1992 ). a hybridoma secreting ucht1 was kindly provided by dr . peter beverly , imperial cancer research fund , and was grown in ascites fluid and purified over immobilized protein a . this is an igg1 . we have more recently prepared a rhesus analog of the above immunotoxin using the anti - rhesus cd3 . di - elect cons . monoclonal antibody fn18 . ( fn18 kindly provided by dr . margreet jonker , biomedical primate research center , rijswijk , netherlands .) f . nooij et al ., 16 eur . j . immunol . 981 - 984 ( 1986 ). fn18 , also an igg1 , is the rhesus analog of ucht1 and shares with it the property of being a t - cell mitogen in the presence of mixed mononuclear cells . fn18 was produced in hollow fiber and purified over protein a . the strain of c . diphtheriae used for production of crm9 , c7 ( βh tox - 201 tox - 9 h &# 39 ;) was obtained from r . holmes , uniformed services university of health sciences , bethesda , md . see also v . hu et al ., 902 biochimicia et biophysica acta 24 - 30 ( 1987 ). antibody - crm9 was recovered from the supernatant of 30 liter fermentation runs under careful control of iron concentration . see s . l . welkos et al ., 37 j . virol . 936 - 945 ( 1981 ). crm9 was purified by membrane concentration , ammonium sulfate precipitation and chromatography over deae . see s . carroll et al ., 165 methods in enzymology 68 ( 1988 ). large scale purification of immunotoxin was accomplished by hplc size exclusion chromatography on modcol ( 1266 andes blvd ., st . louis , mo . 63132 ) 2 &# 34 ;× 10 &# 34 ; column packed with zorbax ® chromatography column bulk packing ( dupont company ) gf - 250 5μm , 150 å . fractions containing 1 : 1 toxin : antibody mol ratios were isolated for these studies . immunotoxins were synthesized as previously described by thiolating both the monoclonal antibody moiety and the toxin moiety and then crosslinking with bismaleimidohexane . see d . neville et al ., 264 j . biol . chem . 14653 - 14661 ( 1989 ). crm9 was nicked and the monomer ( carroll et al .) was isolated by the modcol column described above prior to thiolation . while crm9 is a preferred mutant diphtheria toxin protein , other diphtheria mutants with a mutation in the dt binding region should also be suitable ( as the concept behind the immunotoxin is to replace the normal binding function with the antibody provided t - cell binding function , with minimal conformational change ). monoclonal antibody fn18 ( specific for rhesus monkey t lymphocytes ) coupled to the immunotoxin crm9 was used to deplete peripheral blood t - cells to levels below 200 cells / ml 3 in adult rhesus monkeys ( measured six days after the injection ). some modest b cell depletion occurred . following depletion , complete t - cell recovery takes about three to four weeks in a juvenile rhesus monkey model using this agent . surprisingly , notwithstanding this fast recovery , donor t - cells injected into the thymus still were not impaired in their ability to tolerize . four monkeys received 0 . 2 mg / kg of immunotoxin , in three divided doses ( 24 hours apart from each other ). another monkey received 0 . 133 mg / kg immunotoxin in two divided doses ( 24 hours apart from each other ), and the other monkey received 0 . 1 mg / kg in two divided doses ( 24 hours apart from each other ). two days after the last dose of immunotoxin , all monkeys except the last had at least 80 % ( actually greater than 99 %) depletion of t cells both in the peripheral blood and in the lymph nodes . the lowest dose used in the last monkey reduced , but did not substantially eliminate either peripheral blood or lymph node lymphocytes . table 1 summarizes the outcome of renal transplants performed following thymic injection of donor lymph node lymphocytes ( mixture of t and b cells ) combined with immunotoxin therapy . cells injected intrathymically consisted of the pooled axillary and inguinal lymph node lymphocytes in the numbers listed . table 1______________________________________ interval to # donor trans - anti - cd3 - crm9 graftmonkey lympho - plant lymphoablative survival cause of # cytes ( days ) therapy ( mg / kg ) ( days ) failure______________________________________92099 1 . 6 × 10 . sup . 8 7 0 . 20 8 urine leak93023 7 . 0 × 10 . sup . 8 7 0 . 20 & gt ; 18092049 1 . 4 × 10 . sup . 8 7 0 . 20 13 pneumonia93038 1 . 6 × 10 . sup . 8 0 0 . 133 39 pneumonia92102 0 . 14 × 10 . sup . 8 0 0 . 10 9 rejection92108 1 . 88 × 10 . sup . 8 7 0 . 20 & gt ; 43______________________________________ two monkeys died of pneumonia , one at 39 days and the other at 13 days . a third monkey died at 8 days of complications stemming from a urine leak . at autopsy , none of these three monkeys had any evidence of renal transplant rejection , either grossly or histologically . monkey # 93023 , which received the intrathymic injection and immunotoxin seven days prior to renal transplantation , had normal renal function more than 180 days post - transplant . a renal biopsy of his transplanted kidney at 100 days showed no evidence of rejection . preferred surgical procedures included partial median sternotomy for exposure of the thymus and injection of donor lymphocytes into the thymus gland ; inguinal and axillary lymphadenectomy to procure donor lymphocytes ; laparotomy for procurement of the left kidney from kidney donors ; and a second laparotomy for renal transplantation and native right nephrectomy . all of these procedures will be performed under general anesthesia as outlined below . serial blood draws will be performed under ketamine and xylazine anesthesia as outlined below . thymic injection is performed through a midline chest incision beginning at the sternal notch extending down to the midportion of the sternum . the sternum is divided and retracted to expose the underlying thymus gland . the thymus gland is injected with donor lymphocytes and the sternum reapproximated and the soft tissue closed . donor nephrectomy is performed under general anesthesia through an upper midline incision in the abdomen . the retroperitoneal attachments of the left kidney are divided , the ureter is ligated and divided near the bladder , and the left renal artery and vein are dissected free . the left renal artery and vein are ligated adjacent to the aorta and inferior vena cava , and the kidney excised and flushed on the back table with preservation solution . the recipient operation for renal transplantation is performed by making a midline abdominal incision under general anesthesia . the distal aorta and inferior vena cava are dissected free . the vena cava is clamped proximally and distally near its bifurcation and the donor renal vein anastomosed end - to - side to the recipient inferior vena cava using running 7 - 0 prolene suture . the aorta is cross - clamped proximally and distally just proximal to its bifurcation and the donor renal artery anastomosed end - to - side to the aorta using running 8 - 0 prolene . a ureteroneocystostomy is then performed by making an anterior cystotomy and anastomosing the spatulated tip of the donor ureter to the bladder mucosa using 8 - 0 prolene suture . the cystotomy is then closed . the abdomen is then closed . lymphadenectomy is performed through an approximately 2 cm groin incision for inguinal lymphadenectomy and a similar length incision for axillary lymphadenectomy . the lymph nodes are excised and bleeding points cauterized . the skin is then closed with running 4 - 0 nylon suture . it should be appreciated that kidney transplants are merely an example application . the invention should be suitable for use with a wide variety of organs ( e . g . liver , heart , lung ). lymphocytes to be donated are preferably pooled from axillary and cervical lymph nodes of a single donor . the nodes are harvested , strained through a mesh to separate the lymphocytes , diluted with saline , and then injected . however , instead , a representative &# 34 ; cocktail &# 34 ; of lymphocytes from several primates other than the donor , at least one of which turns out to be the same haplotype as the likely donor , should also work ( if the donor is not available early enough ). for humans , the preferred doses of the immunotoxin are those sufficient to deplete peripheral blood t - cell levels to 80 %, preferably 90 % ( or especially preferably 99 %) of preinjection levels . this should require mg / kg levels for humans similar to those for monkeys ( e . g . 0 . 15 mg / kg to 0 . 2 mg / kg body weight ), which toxicity studies indicate should be well tolerated by humans . the immunotoxin injection should preferably be made within a week or two prior to the donor cell treatment ( albeit there are indications from murine and in vitro studies that even simultaneous application may suffice ). in sum , surprisingly immunotoxins known to severely deplete t - lymphocytes will selectively deplete the host lymphocytes , without interfering with the donor t - lymphocytes ability to cause tolerization . further , the extreme level of depletion caused by this immunotoxin facilitates tolerization . it will be appreciated that the above disclosure relates only to the preferred embodiments . the invention is not so limited . for the full scope of the invention , the claims should be looked to .