Perspectives On Animal Research

Volume 1, Supplement

An Evaluation of Ten Randomly-Chosen Animal Models of Human Disease

Benign Monoclonal Gammopathy (Mice)

(1)

Description of the Model:

Nineteen percent of humans develop benign monoclonal gammopathy (BMG) by the tenth decade of life.(2) Those with BMG have elevations in serum concentrations of homogeneous immunoglobulin (H-Ig), which results from proliferation of a B-cell clone. The condition is known by several names, often used interchangeably, including benign monoclonal gammopathy (BMG), idiopathic paraproteinemia (IP), and monoclonal gammopathy of undetermined significance (MGUS). BMG itself has no associated morbidity or mortality. Thus, while BMG is not a disease, there is evidence that BMG is a precursor of multiple myeloma (MM).(3,4) Because BMG may be a premalignant process, it is of clinical interest.

In his search for an animal model of human BMG, Radl and his colleagues tested the serum of mice from 13 different strains.(5,6) Although all strains exhibited low frequencies of paraproteins with aging, the rate among C57BL mice was the highest. RadL noted, "...high numbers of C57BL mice contained H-IG in their sera, showing a gradual increase in its appearance during aging from 3 percent at 3 months up to 50 percent at 24 months of age."(5) He stated that, because there are many similarities between C57BL/KaLwRij mice with increased H-Ig and humans with BMG, the animal model merits further study.(1)

Criterion I: Concordance between the Animal Model and the Human Disease

Clinical Presentation:

BMG in "normal" C57BL mice appears to parallel human BMG in many respects, including monoclonal paraproteinemia persisting until death, increased frequency with age, IgG predominance, and similar composition of the bone marrow.(1) There are also some differences between human and murine BMG. Humans with BMG tend to have a much higher serum concentration of H-Ig than mice with BMG. Radl suggested, "...lower levels of paraproteins ... in mice may reflect the higher catabolic rate of mouse Ig."(6) In addition, Radl observed that the incidence of BMG in mice is lower in males than in females. He noted, "A survey of published case reports of human IP may indicate that both the survival and the incidence of IP is the reverse of the situation in mice, as far as sex is concerned."(6) Also, Radl found an increased number of plasma cells in lymph nodes of mice with BMG.(5) This has not been reported in humans.

Pathophysiology:

Despite extensive research with humans and animals, the cause of monoclonal proliferation remains unclear. The similarities in clinical presentation indicate that the etiology of BMG in humans and mice is similar. However, there is evidence that human BMG is a premalignant process and that murine BMG is not; this suggests different pathophysiologies. This issue is controversial, and it will be discussed further below.

Criterion II: Citations

Four key articles by Radl described BMG in C57BL mice and correlated this condition with human BMG.(5-8) There were 40 papers in the English literature published from 1975 to 1988 that cited one or more of these articles. Of these 35 (sic) articles, four were studies involving human subjects.

1. Webster et al.(9) described five patients with autoimmune blood dyscrasias and hypogammaglobulinemia. He cited Radl as follows:

It is puzzling that patients with severe hypogammaglobulinemia, who are unable to produce protective levels of antibodies following infection, nevertheless have a high incidence of autoimmune disease. Most patients with late-onset primary hypogammaglobulinemia either lack circulating B cells or have B cells which are probably 'immature'. One possibility is that the B lymphocytes in these patients are prone to spontaneous or virus-induced clonal proliferation. A similar situation probably occurs in benign paraproteinemia.(9)

Although hypogammaglobulinemia is outside the scope of this study of an animal model of human BMG, it is speculative whether the etiology of BMG in mice and hypogammaglobulinemia in these patients is similar. Webster et al. concluded that clinical investigation is needed to settle this issue: "It will therefore be important to establish whether or not the autoantibody is monoclonal in patients presenting in the future with hypogammaglobulinemia and autoimmune disease."(9)

2. Suzuki et al. studied age-related changes in the distribution of immunoglobulin-containing cells in human bone marrow.(10) They noted:

Radl presented a hypothesis that idiopathic paraproteinemia, the frequency of which increases with age, is a consequence of an age-related deficiency in the immune system. Thus the clustering of immunoglobulin-containing cells in the marrow, which increases with age, could be considered to be an early change which may develop into idiopathic paraproteinemia.(10)

Suzuki et al. speculated that changes in immunoglobulin distribution with age may be an early manifestation of BMG, This speculation is based in part on a hypothesis that Radl derived from his animal studies. To date, Radi's theory has not been verified or refuted by clinical findings.

3. Nagler et al. described a patient with eosinophilic fibrohistiocytic lesions of the bone marrow (EFHBM), osteolytic lesions, and monoclonal gammopathy.(11) They cited Radl's work as follows: "In contrast to the malignant B-cell clone or multiple melanoma that elaborates osteoclast-activating factor, which is responsible for bone destruction, benign monoclonal gammopathy is not accompanied by bone lesions."(11) Nagler et al. noted that there have been 12 reported cases of EFHBM. They considered this case to be different, however, in the multiplicity of the lesions. They also acknowledge that, given the prevalence of BMG, its association with EFHBM may have been a coincidence. They also considered that their patient may have had MM, which had not manifested itself fully at the time of publication. Finally, while they cited Radl's work for the absence of bone lesions in BMG, this aspect of BMG had been noted in humans prior to the publication of RadI's animal model research.(12)

4. Parekh et al. cited this murine animal model when he wrote:

The molecular basis for this variation (in galactosylation of N-linked oligosaccharides of human IgG) is not yet known, but it could be due to a naturally age-related expression of B-galactosyltransferase ... activity within all B lymphocytes ... Alternatively, certain clones of B lymphocytes, differing with respect to their N-glycosylation capacity (glycotype), may dominate at different developmental stages of the immune system. The latter is consistent with the increased frequency of idiopathic paraproteinemias during aging.(11a)

Whether or not research with BMG in mice is relevant to these studies is speculative, and more than one theory accounts for the findings.

Criterion III: Historical Impact

BMG does not cause human morbidity or mortality. Consequently, the condition itself is not clinically significant. However, because BMG may be a precursor of multiple myeloma (MM), it is clinically important to understand and diagnose BMG. There is evidence that human BMG may be a precursor of MM and that this is not the case in mice, but the evidence is conflicting. Schmidt and Moller-Petersen observed a significant rate of transition from benign to malignant monoclonal gammopathy: "Most cases of MGUS (BMG) are stable, some are transitory, and about 15% later change into an overt MMG (malignant monoclonal gammopathy), a transition that may occur more than 20 years after detection."(13)

Kyle reported that, of 241 patients who presented with monoclonal protein but no associated disease, 46 (19%) developed serious, related diseases - multiple myeloma (32 patients), Waldenstrom macroglobulinemia (6 patients), systemic amyloidosis (6 patients), others (2 patients).(4)

Other investigators have noted a lower rate of malignant transformation, Axelsson followed 64 patients with serum M-component, and he documented only one definite development of MM.(14) Waldenstrom reported 65 patients with monoclonal IgG, and he found that three had "initial BMG increasing rather slowly to clinical myeloma" and two manifested "BMG with constant levels for some time and then abrupt increase with development of myeloma."(15)

Although there is some evidence of malignant transformation in humans, this does not appear to occur in mice. In 1979, Radi noted:

...in the final stage, a different defect in the intrinsic cellular regulation is likely to take place in each of these two proliferation disorders. In the majority of cases, the if will remain as a 'benign' condition, a consequence, and a symptom of an age related selective immunodeficiency; only in very rare instances, may this B-cell clone become a target for a new mutation and a malignant transformation.(16)

Radl et al. also commented in 1979 that, "...IP represents in its final stage in the aging C57BL mice an intrinsic cellular defect within the affect B cell clone, which is, however, different from that found in B cell malignancies."(7) Tn 1984, Radl again concluded that BMG is not a premyeloma condition in mice: "...the results of hundreds of follow up studies of BMG in the aging C57BL mouse showed no development or transition from BMG to a multiple myeloma..."(17)

Waldenstrom recognized the many similarities of BMG and MM, but he also noted that the issue of malignant transformation is an important one. Waldenstrom wrote:

From many points of view the most important problem has been the question if the monoclonal gammapathies found in certain strains of mice could be compared to similar conditions in man. The group around Radl has presented a very important collection of facts illustrating this problem. It seems clear to me that the similarities between the two groups are so striking that identity may be assumed. This is of course very important because it means that we can use the mice as models in experiments that cannot be performed with patients. It seems probable that, for instance, chromosomal analysis will give us a much better understanding of the basic mechanisms and also illustrate the clinically most important fact if we may find transitions from a static benign condition to a malignant one.(18)

Thus, Waldenstrom endorsed the animal model for the study of BMG. Importantly, if BMG can precede MM, then an understanding of the etiology of BMG may lead to strategies for the prevention or treatment of MM. However, there is strong evidence that murine BMG does not undergo malignant transformation. BMG itself raises issues more related to basic science than to human patients because BMG is asymptomatic.

Has research with murine BMG assisted in the distinction of BMG from MM? This is an important issue because BMG requires no treatment, but MM is responsive to chemotherapeutics. In 1970, four years prior to the development of the animal model, Waldenstrom described clinically useful differences between BMG and MM. He noted:

... a combination of M component (H-Ig) above 2 gm/100 ml, a decreased serum albumin in an afebrile patient as well as Bence-Jones protein in the urine, plasma cell percentages > 10 and marked anemia should increase the suspicion of early myeloma.(12)

He added that radiographic bone lesions were helpful diagnostically.

In 1984, Waldenstrom reviewed the clinical literature on BMG and reported that his original criteria had been refined but essentially remained the same.(15) A constant level of monoclonal immunoglobulin is characteristic of BMG, while rising H-Ig may indicate a malignant process. Plasma cell counts exceeding 10 percent, osteolytic lesions, and Bence-Jones proteinuria help differentiate MM from BMG. In 1987, Griep et al. developed a test to help identify MM. They used human serum and bone marrow samples to determine immunofluorescence labeling indices (LI). They found, "...a high LI (0.8 percent or more) distinguishes patients with newly diagnosed MM from patients with MGUS (BMCJ)."(19)

Clinicians evaluated the clinical impact of the animal model in several recent review articles. Waldenstrom's review of BMG in 1984 focused on efforts to distinguish BMG from MM.(13) They did not refer to the animal model of BMG. There was one reference to a review of in vitro studies using animal cells.

Another paper by Crawford and Cohen on monoclonal gammopathies in elderly populations also did not cite any animal research.(20) Trofatter's review of immune responses and aging did cite Radl's work. Trofatter noted:

Several observations and hypotheses have been made to explain ... the decrease in antibody formation in response to foreign immunogen and the increase in response to self. Radl and Hollander have proposed that the age-related increase in the incidence of monoclonal gammopathy is a result of the loss of the ability to maintain self tolerance with age.(21)

This hypothesis, based in part on animal research, is one of many competing theories, none of which has been proven for human patients.

Conclusions:

There are many similarities between BMG in humans and BMG in C57BL mice, which suggests that human and murine BMG may share a similar etiology. These similarities may assist basic science projects with the murine model, but basic science issues are outside the scope of this study. The animal model does not appear to be very helpful in clarifying the most important clinical issues. BMG may represent a premalignant process in humans, but murine BMG does not appear to be a precursor of MM. Consequently, it does not appear that research with mice that have BMG can demonstrate the process of malignant transformation. (The murine model of MM may be relevant to this issue, but animal models of MM are outside the scope of this review.) Another critical issue is the distinction of BMG from MM. To date, the bases for the diagnosis of BMG and MM have relied on human clinical investigation. Given that there are some differences in the presentation of human and murine monoclonal gammopathies, it appears that human clinical material will remain of primary importance.

References:

1. Radl J: Benign monoclonal gammopathy (idiopathic paraproteinemia), Model no. 234, in Capen CC, Hackel DB, Jones TC, Magaki G (eds): Handbook Animal Models of Human Disease, Fasc. 11. Washington DC, Registry of Comparative Pathology, Armed Forces Institute of Pathology, 1982.

2. Radl J, Sepers JM, Skvaril F, Morell A, Hijmans W: Immunoglobulin patterns in humans over 95 years of age. Clin Exp Immunol 1975;22:84-90.

3. Waldenstrom JG: Benign monoclonal gammopathies, in Azar A, Potter M (eds): Multiple Myeloma and Related Disorders. Hagerstown, Harper and Row, 1973.

4. Kyle RA: 'Benign' monoclonal gammopathy: A misnomer? JAMA 1984;251:1849-1854.

5. Radl J, Hollander CF: Homogeneous immunoglobulins in sera of mice during aging. J Immunol 1974;112:2271-2273.

6. Radl J, Hollander CF, van den Berg P, de Glopper E: Idiopathic paraproteinemia: studies in an animal model-the ageing C57BL/KaLwRij mouse. Clin Exp Immunol 1978;33:395-402.

7. Radl J, de Glopper E, Schniit HRE, Zurcher C: Idiopathic paraproteinemia: Transplantation of the paraprotein-producing clone from old to young C57BL/KaLwRij mice. J Immunol 1979;122:609-613.

8. Radl J: Benign monoclonal gammopathy. Am J Pathol 1981;105:91-93.

9. Webster ADB, Platts-Mills AE, Jannossy G, Morgan M, Asherson GL: Autoimmune blood dyscrasias in five patients with hypogammaglobulinemia: response of neutropenia to vincristine. J Clin Immunol 1981;1:113-118.

10. Suzuki K, Hirokawa K, Hatakeyama S: Age-related change of distribution of immunoglobulin containing cells in human bone marrow. Virch Arch [Pathol Anat] 1984;404:243-251.

11. Nagler A, Ben-Arieh B, Brenner B, Tatarsky I, Pollack S: Eosinophilic fibrohistiocytic lesion of bone marrow associated with monoclonal gammopathy and osteolytic lesions. Am J Hematol 1986;23:277-281.

11a. Parekh R, Roitt I, Isenberg D, Dwek R, Rademacher T: Age-related galactosylation of the N-linked oligosaccharides of human serum IgG. J Exp Med 1988;167:1731-1736.

12.. Waldenstrom JG: Diagnosis and Theatment of Multiple Myeloma. New York, Grune and Stratton, 1970.

13. Schmidt EG, Molter-Petersen J: Monoclonal gammopathy in general practice. Scand J Prim Health Care 1985;3:91-98.

14. Axelsson U: A 20-year follow-up study of 64 patients with M-components. Acta Med Scand 1986;219:519-522.

15. Waldenstrom JG: Benign monoclonal gammopathy. Acta Med Scand 1984;216:435-447.

16. Radl 3: Idiopathic paraproteinemia-a consequence of an age-related deficiency in the T immune system. Clin Immunol Immunopathol 197914:251-255.

17. Radl J: Differences among the three major categories of paraproteinemias in aging man and the mouse-a mini review. Mech Ageing Dev 1984;2&167-170.

18. Waldenstrom JG: Concluding remarks. in Radl J, van Camp B (eds): Monoclonal Gammapathies II: Clinical significance and basic mechanisms. Rijswijk Eurage, 1989.

19. Greipp PR, Witzig TE, Gorchoroff NJ et al.: Immunofluorescence labeling indices in myeloma and related monoclonal gammopathies. Mayo Clin Proc 1987;62:969-977.

20. Crawford J, Cohen HJ: An approach to monoclonal gammopathies in the elderly. Geriatrics 1982(10);37:97-112.

21. Trofatter KF: Immune responses and aging. Clin Obstet Gynecol 1986;29:384-396.