Saturday, July 22, 2006

Monoclonal antibodies 4

George Weiner from Iowa also took as his beginning the fact that polymorphisms of the Fc gamma III receptor (which for ease I will now call CD16) influences response to rituximab in follicular lymphoma and Waldenstrom’s macroglobulinemia and also active immunization with idiotype. NK cells with the high affinity polymorphism are better at ADCC.

Weiner’s group demonstrated that antibody-coated tumor cells modulated CD16 on NK cells, and activated the NK cell as indicated by the upregulation of CD54 and production of interferon-gamma (CD54 is ICAM-1; it mediates cell adhesion by binding to integrins). All these activities are greater for the high affinity polymorphism. As well as mediating ADCC these changes might enhance other immune effects on the target.

They next used molecular means to vary the structure of anti-CD20 antibodies. AME-B showed higher affinity to CD20 and AME-D showed higher affinity to both CD20 and to CD16, (AME stands for Applied Molecular Evolution, a company founded to do just this.)

They demonstrated that AME-D performed better than AME-B or rituximab in the following ways: it induced CD16 modulation, upregulated CD54 on NK cells, and more effectively induced ADCC at lower concentrations of antibody, irrespective of the CD16 polymorphisms of the NK cells. Moreover, this superiority was seen when CLL cells were used as targets (rituximab was unable to induce ADCC of CLL cells under the same conditions). Alas in a mouse xenograft model where Raji cells were grown in immunodeficient mice, no difference was seen between the efficacy of AME-D and rituximab in inhibiting the growth of the cell line.

A second section of the talk dealt with the immunostimulatory effects of CpG oligodeoxynucleotides (ODN). Bacterial DNA is known to be stimulatory to the immune system. Bacterial plasmids are utilized as DNA vaccines. Arthur Krieg from Iowa noted that synthetic ODN containing CpG dinucleotides are even more immunostimulatory.

Weiner’s group demonstrated that incubation of CLL cells with CpG ODN upregulates CD20 and antigen presenting and costimulatory molecules like CD40 and CD80, and enhances expression of both ligands and receptors from the TNF family including Fas, FasL, TRAIL, and TRAIL receptors, which are necessary for the non-mitochondrial pathway of apoptosis. In some samples apoptosis of the CLL cells was induced. Finally, the IL-21 receptor was upregulated.

IL-21 is a regulatory cytokine that increases the activity of NK cells and cytotoxic T cells (CTLs) in killing tumor cells. In vitro analysis of combination treatments demonstrated.

Weiner has demonstrated that IL-21 plus CpG ODN are synergistic in their ability to induce apoptosis of CLL cells. CLL cells treated with IL-21 plus CpG are able to kill untreated bystander cells. They can induce CLL cells to produce functional Granzyme B that is responsible in large part for the observed bystander effect. Antibodies against the B cell receptor plus IL-21 are also synergistic in CLL cells for their ability to induce Granzyme B production and apoptosis and they can induce Granzyme B production by other B cell populations including lymphoma lines, EBV lymphoblasts, and benign B cells.

Granzyme B is a 32-kDa serine protease that is a constituent of the cytotoxic granules in NK cells and CTLs. It is one of the fastest and effective executioners of apoptosis known.

Clearly, the idea of making CLL cells their own executioners is very exciting. CpG and IL-21 are very exciting molecules for CLL patients.

I have delayed writing about this presentation, in deference to George Weiner, as much was unpublished. However, the last of the papers is now e-published in Blood here and here.

Some of the other details have already been published at

Jahrsdorfer et al. Immunostimulatory oligodeoxynucleotides induce apoptosis of B cell chronic lymphocytic leukemia cells. J Leukoc Biol. 2005;77:378-387.

Jahrsdorfer et al. Good prognosis cytogenetics in B-cell chronic lymphocytic leukemia is associated in vitro with low susceptibility to apoptosis and enhanced immunogenicity. Leukemia. 2005;19:759-766.

Jahrsdorfer et al. Serum alters the uptake and biologic activity of CpG oligodeoxynucleotides in B cell chronic lymphocytic leukemia. Oligonucleotides. 2005;15:51-59.

Jahrsdorfer et al. B-cell lymphomas differ in their responsiveness to CpG oligodeoxynucleotides. Clin Cancer Res 2005;11:1490-9.

Finally, finally we had an excellent presentation from Chaya, which I don’t need to summarize because she has already posted a full version of it here.

No comments: