Prognostic Factors for Pediatric, Adolescent, and Young Adult Patients with Non-DIPG Grade 4 Gliomas: A Contemporary Pooled Institutional Experience

PURPOSE/OBJECTIVE(S)

WHO grade 4 gliomas are rare tumors in the pediatric and AYA (adolescent and young adult) population. In this study, we evaluate prognostic factors, toxicities, and outcomes in the pediatric versus AYA population.

MATERIALS/METHODS

This retrospective pooled institutional study included patients < 30 years old with grade 4 gliomas. Overall survival (OS) and progression free survival (PFS) were characterized using Kaplan-Meier and Cox regression analysis.

RESULTS

Ninety-seven patients (n = 20 < 15y, n = 77 ≥ 15y) were identified with a median age 23.9y at diagnosis. Most had biopsy-proven glioblastoma (91%) and the remainder had diffuse midline glioma, H3K27M-altered (9%). All patients received surgery and adjuvant radiotherapy. Median PFS and OS were 20.9 months and 79.4 months, respectively. Gross total resection was associated with better PFS in multivariate analysis [HR 2.00 (1.01-3.62), p = 0.023]. Age ≥15y was also associated with improved OS [HR 0.36 (0.16-0.81), p = 0.014] while female gender [HR 2.12 (1.08-4.16), p = 0.03] and K27M altered histology [HR 2.79 (1.11-7.02), p = 0.029] were associated with worse OS. Only 7% of patients experienced grade 2 toxicity during radiation. Sixty-two percent of patients experienced tumor progression, 28% local and 34% distant. Analysis of salvage treatment found reirradiation was not associated with improved OS, but second surgery and systemic therapy significantly improved survival from the time of tumor progression.

CONCLUSION

Age is a significant prognostic factor in WHO grade 4 glioma, which may reflect age-related molecular alterations in the tumor. Diffuse midline glioma was associated with worse OS compared to hemispheric glioblastoma; this may be related to lack of effective targeted therapies. Surgery and systemic therapy were effective salvage options that significantly improved outcome. Better understanding of prognostic factors may guide future treatment within this understudied patient population, and prospective studies are warranted.

Spine Stereotactic Radiosurgery for Primary and Metastatic Osteosarcoma

PURPOSE/OBJECTIVE(S)

Osteosarcoma is difficult to control due to its high propensity for metastasis and resistance to local and systemic therapies. High doses of radiation therapy (RT) may confer local control (LC) in some settings but for lesions involving the vertebral bodies, proximity to the spinal cord may limit the ability to deliver an adequate dose. In this analysis, we investigate the role of spine stereotactic radiosurgery (SSRS) to overcome this barrier and enable efficacious treatment of primary or metastatic osteosarcoma of the spine.

MATERIALS/METHODS

We retrospectively reviewed all patients treated with SSRS for osteosarcoma of the vertebrae between 2006 and 2022 at a single large tertiary cancer center. We utilized the Kaplan-Meier method to estimate overall survival (OS) and LC.

RESULTS

We identified 18 patients treated with SSRS for 25 lesions of spinal osteosarcoma. Median follow-up was 17.2 months. Two patients and three separate lesions were treated with SSRS for primary osteosarcoma of the vertebrae. The remaining 16 patients and 22 lesions received SSRS to the spine for metastatic disease. Lesions were treated to a dose of 24Gy in one fraction (n = 20) 27Gy in 3 fractions (n = 4) or 50Gy in 5 fractions (n = 1). Treatment sites included the cervical spine alone (n = 4), thoracic spine alone (n = 12), lumbar spine alone (n = 4), sacrum alone (n = 3), or both the thoracic and lumbar spine (n = 2). At latest follow up, local failure was observed in 9/25 (36%) treated lesions and median LC was 22.5 months (95% CI 6-43 months). Per-lesion LC at 1 year was 64% (95% CI 35-83%). Per-patient median OS was 14 months (95% CI 7-68 months) and OS estimates at 1 and 2 years were 60% (95% CI 32-80%) and 35% (11-60%), respectively. Among 15 patients who received 24 Gy in one fraction, at 1 year per-lesion LC was 72% (95% CI 41-88%) and per-patient OS was 60% (95% CI 28-81%). The most common acute treatment related toxicity was pain flare (12%). Four patients (16%) developed compression fractures in the treated vertebrae after radiation, with incidence between 57 and 578 days after radiation. Two of these fractures required intervention and two were incidental findings on imaging. No patients developed CTCAE Grade 3 or higher adverse events including neurological toxicities.

CONCLUSION

SSRS appears to be safe and effective in the treatment of metastatic or primary osteosarcoma involving spinal bone. Future work should include further investigation of this technique with pooled multi-institutional studies and randomized trials.

Phase II Trial of Definitive Therapy for Osseous Oligometastases in Breast Cancer

PURPOSE/OBJECTIVE(S)

Phase II data for consolidative local therapy for oligometastatic disease demonstrated improved outcomes for various malignancies. However, a randomized phase II study of oligometastatic breast cancer patients testing predominantly ablative dose radiotherapy (RT) did not demonstrate progression-free survival (PFS) benefit. We conducted a single-arm phase II trial evaluating local therapy as part of the multidisciplinary management of breast cancer patients with limited bone metastases.

MATERIALS/METHODS

Patients with synchronous (n = 15) and metachronous (n = 15) oligometastatic breast cancer involving ≤3 osseous sites were enrolled from July 2009 to April 2016 and treated to a total of 44 bone metastases. The trial closed early due to slow accrual. Following ≤9 months of systemic therapy, local therapy entailed surgery (n = 3) or RT delivered via conventional fractionation (≥60 Gy, n = 36) or stereotactic technique (27 Gy/3 fractions for spine mets, n = 6). When indicated, RT to the primary was delivered concurrently (n = 15). The primary endpoint was to determine PFS. Secondary endpoints were overall survival (OS), local control (LC) and toxicity. Outcomes were evaluated with Kaplan-Meier and univariate Cox proportional hazards analyses.

RESULTS

Of the 30 patients included in the trial, 23 (77%) had ER+ or PR+/HER2- disease, 4 (13%) had Her2+ disease, and 3 (10%) were triple negative. Median age was 53, and 20 patients (67%) presented with 1 distant metastasis. A total of 21 patients (70%) experienced disease progression at a median 20.5 months (IQR: 8.2-41.2), including 5 local failures among 44 treated bone metastases (11%). At a median follow-up of 76.7 mon (IQR: 45.4-108.8), the median PFS was 37.8 mon, with 2- and 5-year rates (95% CI) of 60% (45-80%) and 32% (19-55%), respectively. The 2- and 5-year OS rates were 93% (85-100%) and 64% (48-85%), respectively, and the 2- and 5-year LC rates were 91% (80-100%) and 71% (51-98%). For patients who achieved LC, median PFS was 47.7 months (IQR 12.2-73.0). Twenty-one patients (70%) received cytotoxic chemotherapy with or without endocrine therapy for newly diagnosed oligometastatic disease. Nine patients (30%) were still alive with no evidence of disease (NED) at a median 96.9 mon (range: 47.7-158.6). PFS was worse among triple negative patients (p = 0.03), with no difference based on synchronous vs non-synchronous presentation (p = 0.10), receipt of cytotoxic chemotherapy prior to definitive therapy (p = 0.08) or Her2+ status (p = 0.21). There were no Grade ≥3 adverse events.

CONCLUSION

Definitive, predominantly conventionally fractionated local therapy was associated with long-term NED status for 30% of patients with oligometastatic breast cancer involving osseous sites, with minimal treatment-associated toxicity. Developing randomized trials for breast cancer subsets may warrant consideration of standard fractionation regimen data and the need for strategies to identify patients who may benefit from definitive local therapy.

Multi-Institutional Phase I Feasibility Trial of Vertebral Body Sparing CSI for Pediatric Brain Tumors

PURPOSE/OBJECTIVE(S)

Craniospinal irradiation (CSI) is an essential part of curative treatment for several pediatric brain tumors. Proton CSI allows for sparing of the organs anterior to the vertebral bodies (VBs), but this technique still includes the entire VB in the target for growing children. providing no advantage in marrow sparing or adverse effects on growth. Advances in proton therapy including Proton Beam Scanning (PBS) allow for delivery of proton CSI with substantial vertebral body sparing (VBS). We sought to determine the feasibility of VBS CSI using PBS based on the effects on tumor control and growth, and the occurrence of grade III/IV hematologic toxicity.

MATERIALS/METHODS

Clinical and treatment characteristics were recorded for 20 pediatric patients with medulloblastoma (n = 14) or germ cell tumor (GCT) (n = 6) who received proton VBS CSI without concurrent chemotherapy or with concurrent single-agent vincristine in a multi-institutional clinical trial. The following standard variables were extracted for each patient: age, histology, radiation dose, chemotherapy regimen, and growth hormone replacement status. Complete blood counts (CBC) with differential and data on height/weight were recorded at baseline pre-RT, weekly during RT, and after completion of cancer treatment. Hematologic toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4 (CTCAE v4).

RESULTS

Median age of 13 male and 7 female patients receiving proton VBS CSI was 10 years (range: 5.1 - 15.1). All GCT patients (n = 6, 30%) received pre-RT chemo. Median CSI dose was 23.4 Gy (range: 21.0 - 37.8), and total dose to tumor bed was 54 Gy in 18 patients (90%) while 2 patients with pure germinoma received a total dose of 36 and 37.5 Gy, respectively. 11 patients (55%) did not receive concurrent vincristine. At a median follow up of 26.4 months (range: 12.5 - 56.3) from the start of RT, no patients relapsed. 17 patients (85%) developed grade ≥3 hematologic toxicity including grade 3 lymphopenia (n = 16), leukopenia (n = 9), neutropenia (n = 8), anemia (n = 1), and grade 4 neutropenia (n = 1). The patient who developed grade 4 neutropenia had low white blood counts prior to RT. 14 patients (70%) received post-RT chemo. No patients required platelet transfusion during RT. Those findings are similar to historical controls. 4 patients started growth hormone replacement therapy after RT. No patients developed spine deformities after the completion of treatment.

CONCLUSION

Proton VBS CSI is a feasible and well tolerated treatment for children with brain tumors. Longer follow up is needed to assess for late effects on tumor control. It is too early to assess for height in this cohort but for the patients that had longer follow up, normal height was achieved.

Early Outcomes from Proton Craniospinal Irradiation (pCSI) for Leptomeningeal Disease from Solid Tumors

PURPOSE/OBJECTIVE(S)

Prospective data suggest that proton craniospinal irradiation (pCSI) improves overall survival (OS) in patients with leptomeningeal disease (LMD) from solid tumors, compared to the historical standard of involved field radiation. To evaluate outcomes of this novel approach in a real-world setting, our institutional experience with treating adults with pCSI for LMD from solid malignancies was evaluated.

MATERIALS/METHODS

On an IRB-approved protocol, medical records of adults with LMD from solid tumors treated with pCSI were retrospectively reviewed for patient, disease and treatment characteristics and outcomes. CNS-PFS and OS were calculated from the last day of pCSI, and survival was modeled using Kaplan-Meier analysis.

RESULTS

From December 2021 to November 2022, 17 patients with median age 51y (range 22-71y) were treated with pCSI for LMD from solid tumors. Thirteen patients (76%) were female. Ten had ECOG PS of 0-1, and seven had PS 2-3. Nine patients (53%) had breast cancer, 3 (18%) had non-small cell lung cancer (NSCLC), 2 (12%) had melanoma, 1 (6%) had colorectal adenocarcinoma, 1 (6%) had endocervical adenocarcinoma, and 1 (6%) had two synchronous primaries (adenocarcinoma of the gastro-esophageal junction and neuroendocrine carcinoma of the lung). All patients had prior radiation; ten had prior radiation to the brain, one had prior radiation to the spine, and six had other sites previously radiated. Fourteen patients (82%) were treated to 30 Gy in 10 fractions and 3 (18%) were treated to 25 Gy in 10 fractions due to overlap with prior radiation fields. Median follow-up was 4 months (range, 1-13 months). Among 15 evaluable patients, median CNS-PFS and median OS were 3.6 months and 4.7 months, respectively. For patients with breast cancer or NSCLC, 62% were alive at 6 months; median OS has not been reached. Treatment was well tolerated with no grade 3-4 non-hematologic adverse events.

CONCLUSION

pCSI is a novel method for treatment of LMD from solid tumors that has been rapidly adopted. Based on our preliminary review, it is safe and well-tolerated; patient selection is critical. As these patients are often heavily pretreated, prior radiation fields must be considered in pCSI planning.

Frameless Fractionated Linear Accelerator-Based Stereotactic Radiotherapy for Brain Metastases: Results of a Single-Arm Phase II Multi-Institutional Clinical Trial

PURPOSE/OBJECTIVE(S)

Stereotactic radiotherapy (SRT) yields high rates of local control for brain metastases while minimizing neurocognitive side effects. While advanced SRT platforms are widely available in urban centers, rural/suburban patients face geographic and socioeconomic barriers to access SRS. For this reason, we conducted a multi-institutional Phase 2 clinical trial to test the safety and efficacy of 3-5 fraction frameless fractionated stereotactic radiotherapy (FFSRT) for brain metastases in an integrated academic satellite network MATERIALS/METHODS: This IRB-approved Phase 2 trial was conducted for patients ≥18-years-old with 1-4 brain metastases. Brain metastases involving the optic pathway or brainstem were excluded. Gross tumor volume (GTV) was delineated with a volumetric brain MRI and planning target volume (PTV) was GTV + 2 mm margin. Radiation dose was based on GTV size: < 3.0 cm, 27 Gy in 3 fractions, and 3.0-3.9 cm, 30 Gy in 5 fractions. Toxicity was evaluated using the Common Terminology Criteria for Adverse Events (CTCAE) version 4.

RESULTS

Of 76 evaluable patients, the median age was 67 years, 56.6% were female, 82.9% were white/Caucasian and 89.6% had an Eastern Cooperative Oncology Group performance status ≤ 2. Most brain metastases were from lung cancer (51.3%) and breast cancer (15.7%). With median follow-up of 10 months, local control was 93%, median survival was 1.8 years (95% confidence interval (CI): 1.5-2.4 years), 1-year OS was 73.8% (95% CI: 0.59-0.84), and 2-year OS was 31% (95% CI: 0.12-0.52). There were no CTCAE Grade ≥ 3 protocol-related adverse events.

CONCLUSION

Outcomes of this trial compare favorably with contemporary SRT trials for brain metastases. FFSRT may provide opportunities to expand SRS access for underserved populations across the MDACC enterprise and in future clinical trials for brain metastases.

Dosimetric Analysis of Local Failure Outcomes and Vertebral Compression Fracture Risk in Single-Fraction Spine Stereotactic Radiosurgery for Metastatic Sarcoma

PURPOSE/OBJECTIVE(S)

Sarcoma spinal metastases (SSM) are particularly difficult to manage given their poor response rates to chemotherapy and their inherent radioresistance. We sought to analyze dosimetric parameters impacting local failure and vertebral compression fracture outcomes in a homogenously treated cohort of patients with SSM treated with single-fraction spine stereotactic radiosurgery (SSRS).

MATERIALS/METHODS

A retrospective review was conducted on a cohort of patients with SSM treated with definitive SSRS at a single tertiary institution. 16-24 Gy was delivered to the GTV and 16 Gy uniformly to the CTV. Kaplan-Meier analysis was conducted to assess time to local failure (LF). The log-rank test was utilized to examine group differences. Patients were censored at time of last follow-up or death. Cox proportionate hazards modeling was used to determine hazard ratios (HR) and their respective 95% confidence intervals (CI).

RESULTS

A total of 66 patients with 96 lesions underwent SSRS for SSM. Median follow-up was 17 months (IQR 8-28). Median age was 55 years (IQR 41-63). The most common histological subtype was leiomyosarcoma (41%) followed by liposarcoma (9%). 81 lesions received 24 Gy to the GTV, 12 received 18 Gy and 3 received 16 Gy. Median GTV and CTV volume was 13.6cc (IQR 5-27) and 51.6cc (IQR 30-80) respectively. 27% of patients had Bilsky 1b or greater disease. 16 of 96 lesions demonstrated progression representing a crude local failure rate of 17% with median time to failure of 8 months (IQR 5-18). The 1-year actuarial progression free survival (PFS) was 89% with a median PFS of 13 months (IQR 16-63). Median overall survival (OS) was 15 months (IQR 8-28) from SSRS. 8% of patients developed vertebral compression fractures at a median of 13 months post SSRS (IQR 7-25). Every 1 Gy increase in GTV minimum dose (DMin) across the range (5.8-25cc) was associated with a reduced risk of local failure (HR = 0.875 [95% CI 0.787-0.974], p = 0.01). Stratifying thresholds for GTV DMin, a local control benefit was seen as low as 12 Gy and higher (HR = 0.329 [95% CI 0.11-0.97, p = 0.044) with a significantly greater magnitude benefit seen at 14 Gy (HR = 0.267 [95% CI 0.09-0.77, p = 0.014) and above 15 Gy (HR = 0.091 [95% CI 0.03-0.41], p = 0.0018). There were no other queried variables besides GTV Dmin associated with local control including: GTV: volume, mean, Dmax, D90, CTV: volume, Dmin, Dmean, Dmax, or D90. There was an increased risk of VCF with increasing CTV DMean (HR = 2.4 [95% CI 1.4-4.1], p = 0.002) and CTV D90 (HR = 2.2 [95% CI 1.2-4.0], p = 0.01); however, no association with GTV parameters.

CONCLUSION

This study represents one of the most homogenously treated and the largest cohorts of patients with sarcoma spinal metastases treated with single-fraction SSRS. Despite inherent radioresistance, SSRS confers durable and high rates of local control in SSM without unexpected long-term toxicity rates. Increasing GTV minimum dose is significantly associated with superior local control with no corresponding increased risk of VCF.

MD Anderson Phase III Randomized Preoperative Stereotactic Radiosurgery (SRS) vs. Postoperative SRS for Brain Metastases Trial

PURPOSE/OBJECTIVE(S)

Postoperative stereotactic radiation therapy/radiosurgery (SRT/SRS) is being evaluated in comparison to Preoperative SRT for brain metastases (mets) in a limited number of prospective clinical trials. Our objective is to address the significant knowledge gap concerning the logistics of preoperative SRT in comparison to postoperative SRT in a randomized controlled study.

MATERIALS/METHODS

Patients with brain mets with at least 1 surgically operable met were randomized (1:1) to Preop vs Postop SRT. In this abstract, we present non-primary endpoint data on the trial concept and logistics of treatment for this data safety monitoring board reviewed study. Patients enrolled had 1-2 lesions resected and <15 lesions treated at time of SRT to best reflect the standard population that receive SRT and surgery at our institution.

RESULTS

From 12/2018 to 12/2022, 99 patients with 1-2 operable brain mets were enrolled and randomized to Preop (n = 49) or Postop (n = 50) SRT. Males represented 56% of the cohort compared to females, and <25% were age 18-49 years, while 27%, 29, and 19% respectively were 50-59, 60-69, and > = 70. The most frequent histologies enrolled were lung (29%), renal cell (15%), melanoma (14%), and breast (11%) cancers. The majority of patients (83%) had 1-4 brain mets on their baseline MRI and 91% subsequently had a single lesion resected. Seventy-nine patients completed both SRT and surgery, while 9% received no therapy due to drop out before study therapy initiation. Among patients receiving both therapies in the combined cohort, 68% received a non-invasive stereotactic radiosurgery instrument to the randomized cavity lesion compared to 32% receiving LINAC based SRT. Treatment of the lesion or cavity with single fraction SRT was 51% in the Preop arm vs 31% in the Postop arm. Multi-fraction (3-5 SRT) was 67% in the Postop cohort in contrast to 47% in the Preop cohort. Time from randomization to RT was 5.6 days and 33.7 days in the Preop and Postop cohorts respectively, and for surgery was 10.2 days vs 12.9 days in the Postop vs Preop cohorts. The average time from RT to surgery was 7.3 days in the Preop arm and 23.5 days in the Postop arm (to allow for incisional healing time).

CONCLUSION

In one of the early initiated randomized prospective cohorts of Preop vs Postop SRT, we demonstrated logistical feasibility with an efficient clinical trial workflow for study treatment. Differences in Preop vs Postop logistics reflect clinical practice differences in time-to-treatment. Therapy with various modalities reflected real-world practice and possibly provider preferences in technique when addressing the nature of delineating cavities and changes in cavity volume with regard to fractionation. Independent of the primary outcomes, our data provides insights in the practical management of patients receiving these two modalities of therapy, and further data at the completion of trial will address relevant primary outcomes.

A prospective phase II randomized trial of proton radiotherapy vs intensity-modulated radiotherapy for patients with newly diagnosed glioblastoma

BACKGROUND

To determine if proton radiotherapy (PT), compared to intensity-modulated radiotherapy (IMRT), delayed time to cognitive failure in patients with newly diagnosed glioblastoma (GBM).

METHODS

Eligible patients were randomized unblinded to PT vs IMRT. The primary endpoint was time to cognitive failure. Secondary endpoints included overall survival (OS), intracranial progression-free survival (PFS), toxicity, and patient-reported outcomes (PROs).

RESULTS

A total of 90 patients were enrolled and 67 were evaluable with median follow-up of 48.7 months (range 7.1-66.7). There was no significant difference in time to cognitive failure between treatment arms (HR, 0.88; 95% CI, 0.45-1.75; P = .74). PT was associated with a lower rate of fatigue (24% vs 58%, P = .05), but otherwise, there were no significant differences in PROs at 6 months. There was no difference in PFS (HR, 0.74; 95% CI, 0.44-1.23; P = .24) or OS (HR, 0.86; 95% CI, 0.49-1.50; P = .60). However, PT significantly reduced the radiation dose for nearly all structures analyzed. The average number of grade 2 or higher toxicities was significantly higher in patients who received IMRT (mean 1.15, range 0-6) compared to PT (mean 0.35, range 0-3; P = .02).

CONCLUSIONS

In this signal-seeking phase II trial, PT was not associated with a delay in time to cognitive failure but did reduce toxicity and patient-reported fatigue. Larger randomized trials are needed to determine the potential of PT such as dose escalation for GBM and cognitive preservation in patients with lower-grade gliomas with a longer survival time.

Metallothionein protects against severe oxidative stress-induced apoptosis of human trophoblastic cells

Oxidative stress induces cellular apoptosis. Many agents producing intracellular oxidative stress, including H(2)O(2) and steroid hormones, have also been found to induce metallothionein (MT) expression. Recently, MT has been recognized as potentially having antioxidant activity. This action may be essential for survival of terminally differentiated cells subject to oxidative stress, such as syncytiotrophoblasts, placental cells producing pregnancy hormones and forming the maternal-fetal barrier. We previously demonstrated an inverse relationship between basal MT expression and apoptotic incidence in the trophoblastic cell line, JEG-3. Using JEG-3 cells transfected with MT in sense or antisense orientation, we have examined here the effect of altered basal MT levels on trophoblastic function and apoptosis following treatment with H(2)O(2) or diethylstilbestrol (DES). Induction of MT mRNA was observed in control and transfected JEG-3 cells following exposure to severe oxidative stress. Changes in the localization of MT protein, however, were apparent after a low oxidative stress challenge. Exposure to H(2)O(2) resulted in a dose-dependent decrease in human chorionic gonadotropin secretion in all JEG-3 cultures regardless of basal MT expression, whereas no change was detected following DES treatment. With respect to apoptosis, a significant protective effect was observed proportional to the basal MT level. These results suggest that although MT does not ameliorate oxidative stress-induced perturbation of some trophoblastic functions, its expression is critical for protection of these cells from severe oxidative stress-induced apoptosis. MT thus appears to act as an anti-apoptotic antioxidant in trophoblastic cells.

Metallothionein overexpression in human trophoblastic cells protects against cadmium-induced apoptosis

Proper functioning of trophoblastic cells is essential for maintenance of the placenta and development of the embryo/fetus. Exposure of trophoblasts to toxic exogenous factors, such as cadmium (Cd), perturbs placental function and affects fetal outcome. Cellular responses to Cd exposure include induction of the metal-binding protein, metallothionein (MT), and initiation of apoptosis. To analyze the functional relationship between cellular MT levels and apoptosis in trophoblasts, we have examined the effects of DNA transfection-mediated alterations in MT levels on trophoblastic function and apoptosis, with and without Cd exposure, using the trophoblast-like JEG-3 human choriocarcinoma cell line. JEG-3 cells stably transfected with human MT-IIa cDNA expression constructs, in either sense or antisense orientation, were unchanged in human chorionic gonadotropin (hCG) production or expression of the apoptotic markers, bcl-2 and CPP-32. However, MT overexpression significantly prolonged the recovery time of intracellular Ca flux, whereas reduced basal MT increased the incidence of apoptosis as determined by morphology and terminal deoxynucleotidyl end labeling (TUNEL) staining. Upon Cd exposure, a dose-dependent decrease in hCG secretion was seen in all JEG-3 cultures, without any correlation to basal MT expression. Basal MT levels, however, significantly affected the extent of apoptosis, the incidence being inversely related to basal MT level. These results suggest that while MT does not ameliorate heavy-metal induced perturbation of some trophoblastic functions, its expression is critical for protection of these cells from Cd-induced apoptosis and could act to maintain placental integrity in cases of maternal Cd exposure.

The immunogenicity of the 7E3 murine monoclonal Fab antibody fragment variable region is dramatically reduced in humans by substitution of human for murine constant regions

A murine monoclonal antibody (7E3) directed against the platelet glycoprotein IIb/IIIa was engineered to reduce immunogenicity by substituting human for murine constant regions. The chimeric antibody is functionally identical to the murine antibody in vitro. Results from clinical trials with 7E3 Fab antibody fragments, however, show that the 7E3 variable region, which elicits the vast majority of the immune response to murine 7E3 Fab, is rendered dramatically less immunogenic (incidence reduced from 17% to 1%) when the identical variable region is linked to human rather than murine constant regions. Neither murine nor human constant regions were highly immunogenic themselves. We conclude that the constant regions of the Fab fragments are critical in modulating the immune response elicited by the linked 7E3 variable region. Because naturally occurring anti-human Fab fragment antibodies are prevalent both in the normal human population and in the patient population studied here, murine 7E3 Fab and chimeric 7E3 Fab may be fundamentally different in their interactions with the human immune system. This difference may be related to the dramatic difference in immunogenicity observed between murine 7E3 Fab and chimeric 7E3 Fab.