Peripheral complement interactions with amyloid ß peptide in Alzheimer's disease: 2. Relationship to amyloid ß immunotherapy.

INTRODUCTION: Our previous studies have shown that amyloid ß peptide (Aß) is subject to complement-mediated clearance from the peripheral circulation, and that this mechanism is deficient in Alzheimer's disease. The mechanism should be enhanced by Aß antibodies that form immune complexes (ICs) with Aß, and therefore may be relevant to current Aß immunotherapy approaches. METHODS: Multidisciplinary methods were employed to demonstrate enhanced complement-mediated capture of Aß antibody immune complexes compared with Aß alone in both erythrocytes and THP1-derived macrophages. RESULTS: Aß antibodies dramatically increased complement activation and opsonization of Aß, followed by commensurately enhanced Aß capture by human erythrocytes and macrophages. These in vitro findings were consistent with enhanced peripheral clearance of intravenously administered Aß antibody immune complexes in nonhuman primates. DISCUSSION: Together with our previous results, showing significant Alzheimer's disease deficits in peripheral Aß clearance, the present findings strongly suggest that peripheral mechanisms should not be ignored as contributors to the effects of Aß immunotherapy.

Peripheral complement interactions with amyloid ß peptide: Erythrocyte clearance mechanisms.

INTRODUCTION: Although amyloid ß peptide (Aß) is cleared from the brain to cerebrospinal fluid and the peripheral circulation, mechanisms for its removal from blood remain unresolved. Primates have uniquely evolved a highly effective peripheral clearance mechanism for pathogens, immune adherence, in which erythrocyte complement receptor 1 (CR1) plays a major role. METHODS: Multidisciplinary methods were used to demonstrate immune adherence capture of Aß by erythrocytes and its deficiency in Alzheimer's disease (AD). RESULTS: Aß was shown to be subject to immune adherence at every step in the pathway. Aß dose-dependently activated serum complement. Complement-opsonized Aß was captured by erythrocytes via CR1. Erythrocytes, Aß, and hepatic Kupffer cells were colocalized in the human liver. Significant deficits in erythrocyte Aß levels were found in AD and mild cognitive impairment patients. DISCUSSION: CR1 polymorphisms elevate AD risk, and >80% of human CR1 is vested in erythrocytes to subserve immune adherence. The present results suggest that this pathway is pathophysiologically relevant in AD.

Direct antilymphoma effects on human lymphoma cells of monotherapy and combination therapy with CD20 and HLA-DR antibodies and 90Y-labeled HLA-DR antibodies.

PURPOSE: Monoclonal antibodies (mAb) in combination and mAbs combined with a radionuclide (radioimmunotherapy) have both been more effective in patients than mAb monotherapy. EXPERIMENTAL DESIGN: Using assays of cell growth and viability, the dose response and temporal characteristics of CD20 (rituximab) and HLA-DR (Lym-1) mAbs, singly and in combination, and of 90Y-conjugated Lym-1 mAb have been characterized in five human lymphoma cell lines (B35M, Raji, SU-DHL-4, SU-DHL-6, and Ramos) spanning Burkitt's to diffuse large cell lymphoma. Although Ramos had a lower HLA-DR density, these cell lines were otherwise selected because of high cell surface CD20 and HLA-DR abundance. Assays of cell growth and death were done using microscopy and trypan blue dye. RESULTS: Lym-1 and rituximab, used singly, showed direct antilymphoma effects; those of Lym-1 were often more potent than those of rituximab. Combinations of these mAbs were more effective, sometimes synergistic, than either mAb singly, even in more resistant SU-DHL-4 cells. Conjugation of 90Y to Lym-1 also augmented potency in all cell lines and overcame resistance to both Lym-1 and rituximab in Ramos cells. CONCLUSIONS: Lym-1 exhibited substantially greater direct antilymphoma effects than rituximab in lymphoma cells in culture. Combination of Lym-1 with rituximab or 90Y increased potency and overcame treatment resistance in lymphoma cells. Greater use of combination therapies of this type to increase potency and range of effectiveness seems likely to improve patient outcome.

Documentation of idiotypic cascade after Lym-1 radioimmunotherapy in a patient with non-Hodgkin's lymphoma: basis for extended survival?

PURPOSE: The purpose of this study was to examine idiotypic cascade mechanisms in the plasma of a prolonged survivor patient with aggressive non-Hodgkin's lymphoma (NHL). It is a follow-up to previously published seminal studies by this laboratory showing survival benefit associated with radioimmunotherapy in NHL patients. Immunoglobulin from the patient's plasma was purified, characterized, and shown to possess the activities expected of idiotypic antibodies. EXPERIMENTAL DESIGN: Plasma from a NHL patient treated with Lym-1 was precipitated with ammonium sulfate and octanoic acid, followed by immunoadsorbant chromatography with solid phase Lym-1 monoclonal antibody to purify Ab2. The last purification step involved the binding of Ab3 to glutaraldehyde-fixed Raji cells, followed by acid elution of Ab3. Proteins were quantified and characterized. Antibody-dependent cellular cytotoxicity activity was determined using a standard (51)Cr release assay. RESULTS: Purified immunoglobulin populations exhibited the characteristics of Ab2beta and Ab3 antibodies. Both showed ability to compete with the binding of Lym-1 to its tumor cell target, and Ab3 showed ability to induce antibody-dependent cellular cytotoxicity. CONCLUSIONS: This study offers direct evidence for initiation of a multilevel idiotypic cascade in a patient undergoing passive monoclonal antibody therapy for NHL. The patient's prolonged disease-free survival may, thus, be understood in the context of the generation of endogenous, self-perpetuating tumor-specific antibodies.

Characterization of human IgG antimouse antibody in patients with B-cell malignancies.

PURPOSE: Immunotherapeutic approaches to cancer offer an attractive adjunct to conventional modalities, although human antiglobulin responses can be an obstacle to repeated treatment. This study of a large number of patients with B-cell malignancies, over an extended period of time, characterized their human antimouse antibody (HAMA) seroconversion. EXPERIMENTAL DESIGN: A total of 617 samples from 112 subjects were analyzed for HAMA titers. Eighty-five patients with B-cell malignancies; 12 breast cancer patients, and 15 volunteers were titered for comparison. Fifty-six B-cell malignancy patients were titered for HAMA throughout Lym-1 radioimmunotherapy (RIT); 29 were titered after a single imaging dose of Lym-1 antibody. RESULTS: Baseline titers did not correlate with subsequent HAMA seroconversion against Lym-1. Only 1 of 29 (3%) of the patients developed HAMA after an imaging dose of Lym-1. Of the RIT trial group, 37 of 56 (66%) never developed HAMA above baseline despite multiple doses. Of those who did (19 of 56; or 34%), the HAMA responses fell into two categories. Thirteen responded rapidly (median of 31 days) and were termed "early responders," whereas 6, termed "late responders," had a median response time of 111 days. Early responders developed higher peak HAMA titers with fewer exposures to Lym-1 and took longer to return to baseline than did the late responders. The frequency of new antiglobulin seroconversion decreased as the number of exposures increased. CONCLUSIONS: Seventy-seven percent of B-cell malignancy patients developed no response or a weak response after multiple doses of mouse Lym-1 antibody. Positive responders occurred in all histology types and fell into two categories differing in seroconversion time and titer, possibly indicative of the initial state of the immune system.

Constitutive expression of proinflammatory complement components by subsets of neurons in the central nervous system.

The brain is largely protected from damage due to infection, trauma, and aberrant processes by the innate immune system. These studies were undertaken to determine whether neurons in normal brains constitutively express complement components. In situ hybridization and immunohistochemical studies with specific riboprobes and antibodies, respectively, revealed that most hippocampal neurons, many pyramidal cortical neurons and cerebellar Purkinje neurons in normal murine brains constitutively express C3, C5 and C6. The constitutive expression by neuronal subsets of components of the complement activation and membrane attack pathways suggests that the complement system represents a "first line" of host defense in the brain.

Survival benefit associated with human anti-mouse antibody (HAMA) in patients with B-cell malignancies.

BACKGROUND: About one-third of patients with relapsed B-cell malignancies develop human anti-mouse antibody (HAMA) following mouse antibody treatment. The purpose of this study was to assess the relationship between HAMA and survival in patients given a mouse anti-lymphoma monoclonal antibody (mAb), Lym-1, directed against a unique epitope of HLA-DR antigen that is up-regulated on malignant B-cells. METHODS: ELISA was used to quantify HAMA in 51 patients with B-cell malignancies treated with iodine-131 (131I) labeled Lym-1. Sera were collected prior to and following radioimmunotherapy (RIT) with 131I-Lym-1 until documented to be HAMA negative or throughout lifetime. Univariate, then multivariate analyses including other risk factors, were used to analyze the relationship of HAMA to survival. The relationships of HAMA to prior chemotherapies and to absolute lymphocyte counts prior to RIT were also assessed. RESULTS: Eighteen of 51 patients (35%) developed HAMA following RIT (range of ultimate maximum titers, 6.6-1,802 microg/ml). Using the time dependent Cox proportional hazards model, maximum HAMA titers were associated with survival (P=0.02). HAMA continued to be significant for survival in multivariate analyses that included known risk factors. In Landmark analysis of 39 patients that survived at least 16 weeks, median survival of patients with HAMA less than 5 microg/ml was 61 versus 103 weeks for patients with HAMA equal or greater than 5 microg/ml at 16 weeks (P=0.02). The median survival of the five patients with highest maximum HAMA titers was 244 weeks. At 16 weeks, there was an inverse correlation between the maximum HAMA titer and the number of previous chemotherapies (P<0.003). Absolute lymphocyte counts prior to 131I-Lym-1 treatment for patients that seroconverted were higher than those for patients that did not seroconvert (P=0.01). CONCLUSIONS: Patients with B-cell malignancies that developed high HAMA titers had longer survival that was not explained by risk factors or histologic grade, suggesting the importance of the immune system.

Human antiglobulin response to foreign antibodies: therapeutic benefit?

Immunotherapies for cancer offer attractive alternatives to conventional therapies although human anti-globulin antibody (HAGA) against the antibody (Ab) administered to the patient can be an obstacle to repeated treatment. Monoclonal antibodies (mAb), whether foreign or human in origin, have been used safely in patients for two decades. Adverse events have not proven to be significant clinical obstacles, although alterations of pharmacokinetic behavior of subsequently administered Ab can lead to less effective therapy. Not only is HAGA safe, but it can be associated with beneficial immunity in patients. Studies have shown that some patients have unexpectedly prolonged survival associated with HAGA. In our own non-Hodgkin's lymphoma (NHL) patients treated with mouse Lym-1 anti-lymphoma mAb, a high human anti-mouse Ab (HAMA) titer was associated with increased survival. The possible mechanisms linking HAMA responses to survival are likely related to Ab generated against the idiotopes of the administered Ab. An induced immune cascade in these patients, including anti-idiotypic Ab (Ab2) and cytotoxic Ab1' or Ab3 probably contributed to survival. In summary, HAGA should not a priori preclude the therapeutic use of Ab for cancer.