Higher-dose and less frequent dendritic cell infusions with PSMA peptides in hormone-refractory metastatic prostate cancer patients.

BACKGROUND: Infusion of dendritic cells (DCs) pulsed with PSMA peptides was considered possible in hormone-refractory metastatic prostate cancer patients both with or without prior treatment with a greater number of DCs and for lesser infusions than previously administered. METHODS: DCs + PSMA peptides in patients undergoing leukapheresis were administered monthly 1-4 times, at rates greater than 20 million DCs in 17 patients not previously treated, and in 11 patients previously treated. RESULTS: Three partial responders and one complete responder were noted in the 17 previously untreated persons. DCs + PSMA peptides averaged 28.5 million cells (range in millions, 21.0-42.3). All responders received 3 or 4 infusions of greater than 22 million cells (3-4 times). In the previously treated group of 11 patients, DCs infused averaged 29.3 million cells (range in millions, 20-40.5). One new responder (bone scan) was noted. Two prior responders continued. Observation times were similar. Toxicity was minimal. CONCLUSIONS: These results suggest that DCs + PSMA peptide infusions can be given with greater numbers of DCs with a lesser number of infusions (1-4 monthly) with no loss of response rates compared to those noted previously, and without increased side effects. In previously treated patients (both relapsing and nonrelapsing), adverse effects were not noted, and new responses can be anticipated to be without harmful side effects. However, the follow-up time, and number of patients in this group, were small.

Follow-up ProstaScint scans verify detection of occult soft-tissue recurrence after failure of primary prostate cancer therapy.

BACKGROUND: A reliable imaging modality is required to uncover occult soft- tissue recurrence after failure of primary prostate cancer therapy. This retrospective study was done to evaluate the ability of the (111)Indium-labeled monoclonal antibody (ProstaScint(R)) scan in detection of prostatic bed recurrence and/or metastases to regional and/or distant lymph nodes. METHODS: One hundred sequential patients were evaluated with repeated ProstaScint(R) scans because of evidence of recurrence during the course of their disease. These 100 patients were followed closely from November 1994 and April 1999, and had concurrent bone scans and serum prostate-specific antigen (PSA) evaluations. They have had hormone therapy (n = 53) and/or experienced a rising PSA after radical prostatectomy (n = 38) or after radiation therapy (n = 56). Scan images were scored 0-3, where score 0 = negative, score 1= prostate bed uptake, score 2 = regional lymph node uptake, and score 3 = distant lymph node uptake. In each patient, the uptake of the follow-up scan(s) was compared to that of the initial scan. RESULTS: The median age was 70 years (range, 45-87), and 23 patients had a positive bone scan. The average PSA was 40.5 ng/ml (standard deviation, 223.5). There was 257 scans representing 100 patients. All patients had at least 2 scans, 35 patients had 3 scans, and 11 patients had 4 scans. No individual exhibited detectable adverse clinical reactions during or after the scan. The findings of the initial and consecutive scans were anatomically consistent in 79%, whereas in 21% there were skip metastases. In 24 patients the lesions progressed by scan and PSA, 10 patients showed progression of scan but no PSA progression, 49 patients showed no change, and 17 patients showed a remission related to adjuvant therapy. CONCLUSIONS: The consistency on repeating the scan (79%) and the high percentage of patients showing persistent uptake at the prostate bed (43%) as well as the percentage of detection of regional nodes (20%) and distant nodes (32%) reflects the importance of using the ProstaScint(R) scan in finding occult recurrences after primary treatment failure of prostate cancer. These results are similar to those reported earlier in autopsy series studies in similar populations.

Follow-up evaluation of a phase II prostate cancer vaccine trial.

BACKGROUND: A phase II trial, involving infusions of autologous dendritic cells (DC) and two human histocompatibility antigen (HLA-A2)-specific prostate-specific membrane antigen (PSMA) peptides, was recently completed. Thirty percent of the participants, including subjects with hormone-refractory metastastic disease, and those with suspected local recurrence of prostate cancer, were identified as clinical responders. This report describes the follow-up evaluation of 19 responders in the two study groups. METHODS: After conclusion of the study, study participants were subjected to follow-up evaluations at 6-8-week intervals. Each responder was reevaluated for response status, and duration of response was determined. RESULTS: Subjects were observed for an average of 291 days (metastastic group, group A-2) and 557 days (local recurrence group, group B), which included the treatment and follow-up periods. The average duration of response was 149 days for group A-2, and 187 days for group B. A majority of responders (11/19; 58%) were still responsive at the end of the current follow-up. CONCLUSIONS: The responses observed may be significant and relatively durable. This study suggests that DC-based cancer vaccines in the future may provide an additional therapy for advanced prostate cancer.

GM-CSF as a systemic adjuvant in a phase II prostate cancer vaccine trial.

BACKGROUND: Recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF; Leukine [sargramostim], Immunex Corp., Seattle, WA) was administered to a subgroup of 44 patients in a phase II clinical trial for prostate cancer using DC pulsed with HLA-A2-specific prostate-specific membrane antigen (PSMA) peptides. Our purpose was to determine if GM-CSF caused any enhancement of patients' immune responses, including enhancement of clinical response to the DC-peptide treatment. This report compares the clinical responses to DC-peptide infusions with and without systemic GM-CSF treatment. METHODS: GM-CSF was administered by subcutaneous injection at a dose of 75 microg/m2/day for 7 days with each of six infusion cycles. Prefilled syringes were supplied to the patients for self-administration. RESULTS: One complete and 8 partial responders were identified among 44 patients who received GM-CSF, as compared to 2 complete and 17 partial responders among 51 patients who did not receive GM-CSF. For patients who received GM-CSF and were tested by delayed-type hypersensitivity (DTH) skin test, 3 cases of improved immune response were identified, compared to 5 cases of improvement in patients who did not receive GM-CSF. The main GM-CSF side effects reported were local reactions at the site of injection, fatigue, pain, and fever. Most reported side effects were of mild severity, with some cases of moderate severity leading to discontinuation of GM-CSF. CONCLUSIONS: Our results suggest GM-CSF as employed in this trial did not detectably enhance clinical response to DC-peptide infusions, or significantly enhance the measured immune response.

Phase II prostate cancer vaccine trial: report of a study involving 37 patients with disease recurrence following primary treatment.

BACKGROUND: A phase II trial was conducted to assess the efficacy of infusions of dendritic cells (DC) and two HLA-A2-specific prostate-specific membrane antigen (PSMA) peptides (PSM-P1 and -P2). This report describes the evaluation of 37 subjects admitted with presumed local recurrence of prostate cancer after primary treatment failure. METHODS: All subjects received six infusions of DC pulsed with PSM-P1 and -P2 at 6-week intervals. Clinical monitoring was conducted pre-, during, and post-phase II study. Data included: complete blood count, bone and total alkaline phosphatase, prostate markers, physical examination, performance status, bone scan, ProstaScint scan, and chest X-ray, as well as other assays to monitor cellular and humoral immune responses. RESULTS: One complete and 10 partial responders were identified from this group based on National Prostate Cancer Project criteria, or on a 50% reduction of prostate-specific antigen (PSA), or on a significant resolution in lesions (biopsy-proven when possible) on ProstaScint scan. CONCLUSIONS: About 30% of study participants in this group showed a positive response at the conclusion of the trial. This study suggests that DC-based cancer vaccines may provide an alternative therapy for prostate cancer patients whose primary treatment failed.

Infusion of dendritic cells pulsed with HLA-A2-specific prostate-specific membrane antigen peptides: a phase II prostate cancer vaccine trial involving patients with hormone-refractory metastatic disease.

BACKGROUND: A phase II trial was conducted to assess the efficacy of infusions of dendritic cells (DC) and two HLA-A2-specific PSMA peptides (PSM-P1 and -P2). This report describes thirty three subjects with hormone-refractory metastatic prostate cancer without prior vaccine therapy history who were evaluated and reported as a group. METHODS: All subjects received six infusions of DC pulsed with PSM-P1 and -P2 at six week intervals. Clinical monitoring was conducted pre-, during, and post- phase II study. Data collected include: complete blood count, bone and total alkaline phosphatase, prostate markers, physical examination, performance status, bone scan, ProstaScint scan, chest x-ray, as well as assays to monitor cellular immune responses. RESULTS: Six partial and two complete responders were identified in the phase II study based on NPCP criteria, plus 50% reduction of prostate-specific antigen (PSA), or resolution in previously measurable lesions on ProstaScint scan. CONCLUSIONS: Over 30% of study participants in this group showed a positive response at the conclusion of the trial. This study suggested that DC-based cancer vaccines may provide an alternative therapy for prostate cancer patients whose disease no longer responds to hormone therapy.

Evaluation of phase I/II clinical trials in prostate cancer with dendritic cells and PSMA peptides.

BACKGROUND: A phase I trial involving patients with advanced prostate cancer was conducted to assess the safe administration of dendritic cells (DC) and HLA-A0201-specific prostate-specific membrane antigen (PSMA) peptides (PSM-P1 or -P2). Thirty-three of the phase I participants were subsequently enrolled in a phase II trial, which involved six infusions of DC pulsed with PSM-P1 and -P2 peptides. METHODS: Clinical monitoring was conducted up to 770 days from the start of the phase I study. Data collected included: complete blood count, bone and total alkaline phosphatase, prostate markers, physical examination, performance status, bone scan, ProstaScint scan, and chest X-ray, as well as assays to monitor cellular immune responses. RESULTS: Nine partial responders were identified in the phase II study based on National Prostate Cancer Project (NPCP) criteria, plus 50% reduction of prostate-specific antigen. Four of the partial responders were also responders in the phase I study, with an average response duration of 225 days. Their combined average total response period was over 370 days. Five other responders were nonresponders in the phase I study. Their average partial response period was 196 days. CONCLUSIONS: The responses observed in the phase I and II clinical trials were significant and of long duration. The partial-responder group included patients who continued to respond from phase I, as well as those who started to respond during the phase II trial.

Measurement of serum prostate-specific membrane antigen, a new prognostic marker for prostate cancer.

OBJECTIVES: To describe current results with Western blot assay for prostate specific membrane antigen (PSMA) using 7E11.C5 antibody and the development of an additional antibody measurement for PSMA by a new sandwich immunoassay. METHODS: A population of patients from a screening group, from a difficult diagnostic group, from a pre- and postoperative radical prostatectomy group, and from a group with metastatic disease followed for a serial period, provided the serum values for a prospective assessment of PSMA by Western blot assay. A new monoclonal antibody was sought, reacting to the C-terminal region of PSMA in order to develop a sandwich radioimmunoassay. RESULTS: PSMA values in screened patients correlate with the more advanced stage of the cancers determined. In postprostatectomy patients, the PSMA value corresponds more with preoperative values and with the values of those with a poor clinical course. In difficult diagnostic cases, the PSMA value is increased, specifically in hormone-refractory cases and particularly in those cases judged by other criteria, such as the National Prostatic Cancer Project, to be in clinical progression compared with those judged to be in clinical remission. The level of PSMA value appears to be independent of homogeneous tumor volume and to be more related to that of prior hormone treatment, or to where prostate cancer cells can be documented to be outside the prostate. A new monoclonal antibody, 3F5.4G6, reacts with the extracellular domain of PSMA near the C-terminal region. This is in contrast to the previously measured antibody 7E11.C5, which reacts with an N-terminal epitope. 3F5.4G6 recognizes the same PSMA protein as does 7E11.C5. The epitopes are essentially at opposite ends of the molecule. The 3F5.4G6 antibody reacts with the LNCaP line but not with DU145, or PC3. These two antibodies to PSMA are well suited for use in a new sandwich immunoassay. CONCLUSIONS: PSMA provides a prostatic cancer serum test by using Western blot, which suggests a clinical prognostic value not seen with other markers. New antibodies, such as 3F5.4G6, reacting with the extracellular domain of PSMA combined with 7E11.C5, appear to offer an opportunity for a new sandwich immunoassay.

Report of immune monitoring of prostate cancer patients undergoing T-cell therapy using dendritic cells pulsed with HLA-A2-specific peptides from prostate-specific membrane antigen (PSMA).

BACKGROUND: In this paper we describe our program for the immune monitoring of phase II participants given dendritic cell (DC)/prostate-specific membrane antigen (PSMA)-based immunotherapy, and we also present some initial findings. METHODS: Phase II subjects received six administrations of autologous dendritic cells exogenously pulsed with two peptides derived from PSMA. Prior to the initial infusion, and following each treatment, peripheral blood mononuclear cells (PBMC) were collected for the generation of dendritic cells as well as for comprehensive immune monitoring. RESULTS: Thus far, an increase in PSMA-peptide-specific as well as overall cellular reactivity has been observed in several patients receiving DC plus PSM-P1 and -P2, as measured by delayed-type hypersensitivity (DTH) test and enzyme-linked immunosorbant assay (ELISA). CONCLUSIONS: Our initial observations using an ELISA and DTH test indicate that we are enhancing cellular immunity in prostate cancer patients following infusion with DC plus PSMA-derived peptides. Several methods are underway to comprehensively monitor both cell-mediated and humoral immune responsiveness, including: determining anti-PSMA serum antibody titers, testing immunogen-restricted responder-cell proliferation and cytotoxicity, assessing aberrations in signal transduction, antigen processing, and presentation, and measuring soluble factors that may promote tumor outgrowth.

Comparison of serum PSMA, PSA levels with results of Cytogen-356 ProstaScint scanning in prostatic cancer patients.

BACKGROUND: Stored serum from clinical trial cases undergoing ProstaScint (CYT-356) scanning were available for Prostate Specific Membrane Antigen (PSMA) assay. Prostate Specific Antigen (PSA) levels had already been determined. This provided an opportunity to see what correlations existed between the serum markers and the ProstaScint scan. A group of patients had the studies preprostatectomy, whereas another group had the studies postprostatectomy. METHODS: The scan results, serum PSA, serum PSMA, and clinical data were separately analyzed. PSMA serum levels were determined by Western blot. RESULTS: Preoperatively, radical prostatectomy patients showed a correlation between serum PSA or PSMA levels and the ProstaScint scan in the total group (n = 86), or in an untreated group (n = 38). Preoperatively, PSMA correlated with the pathological stage, whereas PSA correlated with the scan. Postoperatively, only PSMA serum levels correlated with the scan in an untreated group (n = 40). CONCLUSIONS: Preoperatively or postoperatively, Western blot PSMA serum levels predict the stage of disease or local, regional, or distant metastases, as shown by ProstaScint scan. Both the scan and the serum tests provide prognostic information and evaluate the extent of disease to a more significant degree than previously possible.

Brachytherapy for clinically localized prostate cancer: results at 7- and 8-year follow-up.

In recent years, there has been a resurgence of interest in interstitial radiation as a cost-effective and efficient method of treating organ-confined prostate cancer. We describe our 7- and 8-year results with transperineal Iodine-125 and Palladium-103 implantation. A total of 551 consecutive patients were treated. Of these, 320/551 (58%) received implant alone (Group I), and 231/551 (42%)--considered higher risk patients--were also treated with a modest dose (45 Gy) of external beam irradiation (Group II). The median follow-up for Group I was 55 months, and for Group II, 60 months. At 7 years, the actuarial freedom from biochemical failure (prostate-specific antigen (PSA) < or = 1.0 ng/mL) was 80% in Group I patients, and, at 8 years, 65% in Group II patients. Morbidity was minimal if patients had not undergone prior transurethral prostate resections. The results indicate that interstitial radiation is a valid treatment for clinically localized prostate cancer.

Evaluation of PSA, free PSA, PSMA, and total and bone alkaline phosphatase levels compared to bone scans in the management of patients with metastatic prostate cancer.

BACKGROUND: Metastatic prostate cancer clinical evaluation is difficult. A revaluation of new prostate markers with regard to bone scans was performed. METHODS: Serial markers, including bone alkaline phosphatase (BAP), total alkaline phosphatase (TAP), prostate-specific antigen, total (PSA) and free (fPSA), and prostate-specific membrane antigen (PSMA), were obtained in patients under evaluation and treatment for possible or known metastatic prostate cancer. These were correlated with bone scan results (BSR). RESULTS: Seventy patients were observed from mid-October 1996-January 1997, during which time 171 serum samples were obtained and correlated with semiquantitative bone scan status. PSA and fPSA provided some correlation with BAP and BSR, but only at high levels (> 16-50 ng/ml). Receiver-operating curve (ROC) analysis demonstrated that BAP and TAP had a significant discriminating ability for positive and negative bone scans (> .78), compared to PSMA, PSA, and fPSA. However, percent BAP and TAP only correlated with BSR at a level above six lesions. As the lesions detected by BSR increased, the correlation increased. CONCLUSIONS: BAP is a valuable marker for clinical response evaluations to use in the serial follow-up of patients with metastatic prostate cancer, and correlates well with the bone scan as the number of lesions increase to > 6. PSA or fPSA show comparable results, but only at high levels (> 16-50 ng/ml).

Follow-up evaluation of prostate cancer patients infused with autologous dendritic cells pulsed with PSMA peptides.

BACKGROUND: We recently conducted a phase I clinical trial administering autologous dendritic cells pulsed with prostate-specific membrane antigen (PSMA) peptides to advanced prostate cancer patients. Participants were divided into 5 groups receiving 4 or 5 infusions of peptides alone (PSM-P1 or -P2; groups 1 and 2, respectively), autologous DC (group 3), or DC pulsed with PSM-P1 or -P2 (groups 4 and 5, respectively). Seven partial responders were observed. Follow-up evaluation of these responders is presented in this report. METHODS: Clinical monitoring for hematological studies and prostate markers was conducted up to 370 days from the start of the phase I study. Data collected include: lymphocyte, hematocrit, alkaline phosphatase, prostate-specific antigen (PSA), free PSA, and PSMA levels. RESULTS: Groups 4 and 5 (patients infused with DC pulsed with PSM-P1 or -P2) represented 5/7 responders. The length of response was between 100 days (1 patient) to 200 days or above (6 patients). Four patients still remained responsive at the end of the period of observation. CONCLUSIONS: The responses observed in this phase I clinical trial are significant and of long duration. Most of the responders were in treatment groups infused with DC pulsed with PSM-P1 or -P2, suggesting the requirement of both components for effective immunotherapy.

Transrectal ultrasound microbubble contrast angiography of the prostate.

BACKGROUND: Prostate cancer, suspected by serum prostate-specific antigen (PSA) elevation and/or digital abnormalities, is not always evident on gray-scale or color Doppler transrectal ultrasound (TRUS). EchoGen (Sonus Pharmaceuticals, Inc., Bothell, WA), a blood vessel image enhancer able to visualize smaller, low-flow vessels and thus possibly the microvascular angiogenesis often associated with cancer, was employed to see if it would improve prostate cancer detection, particularly in patients with a rising serum PSA and prior negative biopsies. METHODS: Color Doppler TRUS was performed before and after intravenous injection of 0.05 ml/kg of EchoGen. Random and/or specifically directed sextant TRUS biopsies were performed. RESULTS: Fifteen patients with serum PSA elevations were included in the study. Fourteen had a negative prior biopsy (1-3 x). Prostate cancer was detected in 5 patients. Microvascular patterns were judged abnormal in 8 patients, 2 of which proved malignant, 2 of which were benign, and 1 of which was diagnosed with prostatis. False-negative results were observed in 3 patients, whose positive biopsy sites were from the prostate apex. CONCLUSIONS: Following EchoGen administration, prostate blood vessel image enhancement was noted in all patients, and there were no adverse reactions during or after EchoGen administration with the dose employed.

Interstitial iodine-125 radiation without adjuvant therapy in the treatment of clinically localized prostate carcinoma.

BACKGROUND: This study was designed to evaluate the efficacy of iodine-125 interstitial radiation in the treatment of prostate carcinoma classified as T1 or T2. METHODS: One hundred twenty-six consecutive patients with adenocarcinoma of the prostate (T1, 23%; T2, 77%) were treated with iodine-125 radionuclides between January 1, 1988, and December 31, 1990. Four patients died of intercurrent illness within 1 year postimplant, leaving 122 men in the study. The prescribed minimum radiation dose was 160 gray. Median follow-up was 69.3 months. Prebiopsy prostate specific antigen (PSA) values (median, 5.0 ng/mL) were available for all patients. Posttherapy evaluation included clinical, biochemical (PSA), and pathologic (repeat needle biopsy) studies. No patient was surgically staged, and none received androgen deprivation therapy. Morbidity was graded according to the Radiation Therapy Oncology Group grading scale. Statistical appraisal was performed by the Kaplan-Meier method. PSA failure was defined in two ways: (1) PSA progression, i.e., 2 consecutive increases from a nadir value; and (2) failure to attain an arbitrary serum PSA value of 1.0 or 0.5 ng/mL at last follow-up. RESULTS: The overall 7-year survival was 77%; there were no deaths from prostate carcinoma in this cohort. The 7-year actuarial PSA progression free outcome was 89%, and the PSA < or = 1.0 ng/mL outcome was 87%. When PSA < or = 0.5 ng/mL was selected as an outcome end point, and PSA values in this series of radiation-treated patients were compared with PSA values proposed to indicate disease free survival after radical prostatectomy (PSA < or = 0.3-< or = 0.6 ng/mL), the 7-year actuarial disease free survival was 79%. Morbidity was minimal except in patients who had preimplant or postimplant transurethral prostate resection. CONCLUSIONS: Outpatient-based iodine-125 prostate brachytherapy for prostate carcinoma classified as T1 or T2 resulted in biochemical outcomes comparable to end points resulting from radical prostatectomy and external beam radiation.

Cancer immunotherapy for prostate cancer.

Our approach to prostate cancer immunotherapy involves two components dendritic cells as antigen-presenting cells; and the antigen used to target T-cell attack, HLA-A0201-associated peptides from prostate specific membrane antigen (PSMA). We have conducted a phase I dose-ranging study in 51 men with advanced prostate cancer, using dendritic cells pulsed with a PSMA peptide. no significant toxicity was observed. In that study, T-cell response was enhanced, with seven men meeting NCPC and PSA criteria for partial response. We are now conducting a phase II study with 67 men, who will receive 6 infusions of dendritic cells that have been pulsed with 2 PSMA peptides, at 6-week intervals. The phase II study design and rationale is described in this paper.

Evaluation and comparison of two new prostate carcinoma markers. Free-prostate specific antigen and prostate specific membrane antigen.

BACKGROUND: Two new prostate cancer markers, free-prostate specific antigen (f-PSA) and prostate specific membrane antigen (PSMA) were recently introduced. This report summarizes a prospective two-year multicenter test of their diagnostic or prognostic capabilities. Total PSA was also measured. METHODS: There were four clinical groups studied: (1) 226 individuals from a screening project undergoing ultrasound and biopsy evaluation had markers obtained: (2) 68 patients suspected of having prostate cancer and undergoing 2 or more biopsies had the markers obtained on multiple occasions: (3) 100 patients undergoing radical prostatectomy had markers obtained pre- and post-operatively: and (4) 31 patients with metastatic prostate cancer each had multiple samples for marker assay obtained over a 2-year period. In all, 465 patients had one or more samples obtained and studied. RESULTS: Free-PSA affords little additional diagnostic advantage compared with total PSA in the screening population. The receiver operating characteristic curves for diagnostic accuracy were ranked: (1) PSA density; (2) total PSA; (3) f-PSA; and (4) PSMA, PSMA showed the best correlation with stage of the primary tumor in the screened group. In the multiple negative biopsy group, f-PSA varied from 12 to 21%. PSMA values were evaluated in all histologic categories. PSA density was > or = 0.15 in all categories. In the prostatectomy cases PSA values postoperatively were quite low in Stage II; f-PSA was of no value. Later, f-PSA was increased in association with elevated total PSA values. Mean PSMA values were above normal in all postoperative time periods except in Stage III patients at 6 months to 1 year postoperatively. PSA densities were all > or = 0.15. In patients with metastatic carcinoma, elevated PSMA values correlated best with a poor prognosis (clinical progression), as has been described. CONCLUSIONS: These data suggest that f-PSA values do not provide additional diagnostic benefit compared with total PSA in screening populations, in the presence of suspected cancer, postprostatectomy, or in metastatic disease. PSMA is of prognostic significance, especially in the presence of metastatic disease, and correlates well with the stage of disease in cancers detected in a screened population.

Measurement of prostate-specific membrane antigen in the serum with a new antibody.

Work to date has identified prostate-specific membrane antigen (PSMA) as a membrane-bound glycoprotein with high specificity for prostatic epithelial cells. PSMA reacts with the monoclonal antibody 7E11.C5, which is present in serum, seminal fluid, and prostatic epithelial cells, and is increased in its expression in the presence of a hormone refractory state associated with prostatic cancer. This report confirms these results and further documents the presence of the monoclonal antibody 3F5.4G6, which reacts with the extracellular domain of PSMA. This region of PSMA is also an element present in a truncated version of the protein, so-called PSM'. Immune precipitation with either 7E11.C5 or 3F5.4G6 yields an isolated protein species that are reactive with the reciprocal antibody in Western blot analysis. Thus, 3F5.4G6 recognizes the same PSMA protein as does 7E11.C5, but at different epitopes on essentially opposite ends of the molecule. These two antibodies are well suited for use in a sandwich immunoassay, either one as a capture or detection antibody. Current work on this is underway. This report also confirms that 7E11.C5 Western blots for PSMA are negative with normal human brain tissue. The monoclonal antibody 9H10 does not react with 3F5.4G6 or with 7E11.C5 in studies conducted herein. Moreover, 3F5.4G6 reacts with PSMA found in the LNCaP cell line, but not DU-145 or PC3, which lack PSMA.