Immunoglobulin light chain mutational status refines IGHV prognostic value in identifying CLL patients with early treatment requirement

[AussieNeil]

Most of us would be aware of the prognostic value of the immunoglobulin heavy-chain variable region gene (IGHV) mutation status of our CLL (See healthunlocked.com/cllsuppo... for the history.) In general, IGHV mutation status has the greatest influence on our journey with CLL. Roughly 50% of us diagnosed with CLL are fortunate enough to be IGHV mutated and are thus likely to have a long period in watch and wait, so have a greater hope of falling into the group of around 30% of us who never need treatment. Those of us with unmutated IGHV CLL have most benefited from the recent revolution in CLL treatments away from chemoimmunotherapy 'chemo', to targeted treatments. It's the immunoglobulin structure in B Cell Receptors (BCRs) that enable memory B cells to quickly detect and respond to threats to our health and change to the mature plasma cell B cell stage, where they become immunoglobulin manufacturing factories. CLL cells appear a lot like memory B cells; they rely on signalling through their BCRs to stay alive. Without that signalling, they eventually die, which is why BTK inhibitors, the 'brutinibs' and PI3K inhibitors, the 'lisibs', are so effective at controlling CLL.

The accompanying image shows the protein structure of IgG and the stylised representation with which we are most familiar. Our immune system relies on a process termed somatic hypermutation to change the DNA we inherit - our germ line DNA, so that B cells can match the billions of different proteins found in invaders and recognise them for neutralisation and destruction. Somatic hypermutation is the purposeful change to our B cell DNA by which a major part of our adaptive immune system functions, rather than an unwanted cancer causing mutation. Basically, by deliberately mutating our B cell DNA to randomly change the amino acids used to make the heavy and light chain proteins in the immunoglobulin molecule, some B cells in our nodes will key with the invader's proteins and go on to produce plasma cells and memory B cells.

That long introduction brings me to the reason for this post, this article in Nature, brought to my attention by CLLerinOz nature.com/articles/s41375-...

From the abstract, with my emphasis;

The mutational status of immunoglobulin (IG) light chain genes in chronic lymphocytic leukemia (CLL) and its clinical impact have not been extensively studied. To assess their prognostic significance, the IG light chain gene repertoire in CLL patients has been evaluated using a training-validation approach. In the training cohort (N = 573 CLL), 92.5% showed productive IG light chain genes rearrangements, with IGKV4-1 (20.5%) and IGLV3-21 (19.0%) being the most common. A 99.0% somatic hypermutation cut-off was identified as the best predictor for time to first treatment (TTFT) in 414 Binet A CLL patients of the training cohort. Patients with unmutated (UM) light chain genes displayed a 10-year treatment free probability of 32.4% versus 73.2% for those with mutated (M) genes (p < 0.0001). Importantly, UM light chain genes maintained an independent association with a shorter TTFT when adjusted for the IPS-E prognostic model variables, that also includes IGHV mutational status. The validation cohort of 343 Rai 0 patients confirmed these findings, with UM light chain genes predicting a 7-year treatment free probability of 42.0% versus 73.7% for M genes (p < 0.0001). These results indicate that the mutational status of the light chain genes is an independent predictor of shorter TTFT in early-stage CLL patients.

This was a relatively large study for CLL research and the study group was deemed representative of newly diagnosed patients;

The patient characteristics of the training cohort (n = 573) at the time of diagnosis were consistent with a real-world cohort of unselected newly diagnosed CLL (Table 1), since the median age at diagnosis was 70 years, 58.8% were male and 41.2% were females, the median lymphocyte count was 9800/μl, 35.8% had unmutated (UM)-IGHV, 43.5% had del, (13q) 8.0% harbored del (17p) and 9.8% presented TP53 mutations.

To what extent these study results will later be included in regular prognostic testing and beyond, is yet to be seen, but it does further explain why CLL is such a heterogeneous illness.

As I mentioned earlier, the revolution in CLL treatment to targeted therapy came out of research into what could be done to switch off (inhibit) B Cell Receptor signalling. That revolution has resulted in the approval of ibrutinib, acalabrutinib, zanubrutinib and pirtobrutinib, with many more BTKi drugs also in clinical trials, per this post healthunlocked.com/cllsuppo...

PI3K inhibitors, such as idelalisib, duvelisib, umbralisib, zandelisib, et al, also covered in the above post, have unfortunately been less successful.

Our antibody levels and their impact on our ability to fight of infections, are also of relevance, because of how CLL suppresses plasma cell antibody production. That's why hypogammaglobulinemia (low IgA, IgG, IgM) is fairly common when we have CLL and unfortunately tends to worsen over time.

For those interested in further reading about antibodies/immunoglobulins;

Antibody Structure, classes and functions (the lower structural image of IgG is derived from this reference).

antibodysystem.com/archive/...

The IgG molecule visualisation is from the Wikimedia collection commons.wikimedia.org/wiki/...

Antibodies are immune system-related proteins called immunoglobulins. Each antibody consists of four polypeptide – two heavy chains and two light chains joined to form a "Y" shaped molecule.

The amino acid sequence in the tips of the "Y" varies greatly among different antibodies. This variable region, composed of 110-130 amino acids, give the antibody its specificity for binding antigen. The variable region includes the ends of the light and heavy chains.

The structure of a typical antibody molecule

ncbi.nlm.nih.gov/books/NBK2...

Antibodies are the secreted form of the B-cell receptor. An antibody is identical to the B-cell receptor of the cell that secretes it except for a small portion of the C-terminus of the heavy-chain constant region. In the case of the B-cell receptor the C-terminus is a hydrophobic membrane-anchoring sequence, and in the case of antibody it is a hydrophilic sequence that allows secretion. Since they are soluble, and secreted in large quantities, antibodies are easily obtainable and easily studied. For this reason, most of what we know about the B-cell receptor comes from the study of antibodies.

Structure and characteristics of antibody isotypes

Human antibodies are classified into five isotypes (IgM, IgD, IgG, IgA, and IgE) according to their H chains, which provide each isotype with distinct characteristics and roles.

ruo.mbl.co.jp/bio/e/support...

Immunoglobulin vs Antibody: Unveiling the Intricacies

assaygenie.com/blog/immunog...

In the realm of immunology, the terms "immunoglobulin" and "antibody" often find themselves used interchangeably, sparking confusion among those keen on understanding the immune system's fine details. While closely related, these terms encapsulate nuances vital for a comprehensive grasp of how the body defends itself against pathogens.

:

While every antibody is an immunoglobulin, not every immunoglobulin serves as an antibody. This distinction hinges on the function and specificity of the immunoglobulin in the immune response.

Neil

[Floxxy]

Thank you so much Neil. So interesting and well explained. I'm IGHV unmutated, currently on R and V. I saw my consultant last week and she said that I should get a good remission on completion of my 2 years on R and V. X

[Zia2]

As much as I’ve tried, I’ve been unable to understand the light chain, heavy chain, articles and discussions over the past decade. My CLL specialist had my mutation status checked twice with no results. Perhaps Dr. Byrd will come up with an answer. Is that still possible after treatment? I was diagnosed at 54 (one month shy of 55) and needed treatment within 5 years. Is this considered a short or long time? Thanks Neil

[AussieNeil Partner Administrator in reply to Zia2]

IGHV mutation status is very unlikely to change, even after treatment. If yours has changed, then the latest result is what matters.

If you have your flow cytometry results from your initial diagnosis and it includes your CD38 marker status, being CD38 negative increases your likelihood of being IGHV mutated. Likewise if you have ever had your ZAP-70 mutation status checked, again ZAP-70 negative correlates with being IGHV mutated.

That you managed 5 years in watch and wait and have managed a further 3 years in remission since stopping BTKi maintenance treatments, also puts you more likely into the IGHV mutation group. You'll need a reasonable amount of CLL cells for retesting, which you will probably have by now. It's a bit of a mystery as to why your earlier IGHV testing was inconclusive.

Neil

[Zia2 in reply to AussieNeil]

Thank you. I do believe I remember CD38 being negative. I’ll look for sure. Appreciate the response.

[MizLeelee in reply to Zia2]

Hi Zia2, if you find that instead you are CD38+, you could still be mutated. (I have this combo myself -- CD38+, but mutated IGHV). I saw a study that suggested 28 percent of CLL folks have this "discordant" expression.

[wellbeingwarrior in reply to AussieNeil]

The one time I managed to get bloods sent to Australia to test for IGHV status at a cost of $500 .. it came back inconclusive 😜

[BigDee in reply to Zia2]

Hello Zia2

I have had two IGHV tests which results has not changed; I suspect the additional last test was an attempt to cross check because my CLL is so aggressive. Results were both 0% unmutated. I have however had a IGHV blood test which did not have enough sample to be of value. One test specimen was destroyed due to improper transport and storge. Blessings.

[Spark_Plug]

Invaluable!

[DanBro1]

This is a great post! A little on the technical side, but still very readable and informative for a non-medical lay person like myself. This group is lucky to have a person like you on board...

[Bluesinthenight]

Fascinating finding that light chain mutational status adds independent prognostic information to heavy chain (IGHV) mutational status. Further analysis of these findings (perhaps reported in the full publication) would provide the occurrence proportions and the prognostic significance of M-IGHV plus mutated (M) immunoglobulin light chains compared with one or the other UM. Which region provides the greater prognostic significance? Does M-light chain status counteract UM-IGHV status and bring overall prognosis to that of M-IGHV? And vice versa. Does M-IGHV plus M-light chain status provide the best prognosis for delaying or avoiding the need for treatment?

Here it is, reported in the manuscript: ( For the training set)

Therefore, TTFT was evaluated according to the combined heavy and light chain mutational status. CLL patients expressing both UM light chain genes and UM heavy chain genes associated with shorter TTFT (10-year treatment free probability of 13.6%) compared to patients with both M light chains and M heavy chains (10-year treatment free probability of 76.1%, p < 0.001). Discordant cases showed an intermediate outcome (10-year treatment free probability of 54.3%) that significantly differs from that of CLL expressing either concordantly M or concordantly UM heavy and light chain genes (p = 0.01 and p < 0.001, respectively) (Fig. 2B).

and for the validation set:

Subsequently, TTFT was evaluated according to the combined heavy and light chains mutational status and results superimposable to the training cohort were obtained. CLL patients expressing both UM light chain genes and UM heavy chain genes had a 7-year treatment free probability of 35.9%, patients with both M light chain genes and M heavy chain genes had a 7-year treatment free probability of 75.4%, and discordant cases had a 7-year treatment free probability of 60.6% (p < 0.001)

An important finding though is the mutational status of light chain genes and heavy chain genes in the same patient, ie. how often they are the same or different:

Parallel assessment of the mutational status of the light chain genes and its corresponding heavy chain gene in the same patient was performed using the 99.0% cut-off set in this study for light chain genes and the standard 98% cut-off of identity for the heavy chain genes. This analysis showed that mutated IGHV rearrangements associated wthM light chain rearrangements and vice versa (p < 0.0001). More precisely, 83.42% of M-IGHV patients also harbored M lichains, while only 16.6% harbored UM light chains. Conversely, 73.3% of UM-IGHV patients also harbored UM light chains, while 26.7% harbored M light chains (Fig. S5A). Superimposable results were obtained by considering separately kappa and lambda expressing patients.

But still, the study provides some evidence (really an explanation for what we already know!) that unmutated IGHV and mutated IGHV groups have variable prognoses within each group , not uniformly favorable or unfavorable to the same extent, depending on other factors, many of which are yet to be discovered. It appears that light chain gene mutational status is one of these factors.

The underlined text are my comments, BOLD is my emphasis.

Another important point about this article made by the authors in their discussion:

With 11 year follow up of the 500+ patients in the training cohort, most received chemoimmunotherapy with fludarabine as first treatment, so analysis of overall survival and other treatment related outcomes would not be informative in the era of BTK, BCL2 inhibitors and other modern treatments for CLL. So, the Time To First Treatment (TTFT) endpoint they chose was the best and not dependent on treatment type or choice.

[beanlake14]

This is an amazing article and interpretation. Thank you. Please keep sharing with us. I love the science behind our disease

[Smakwater]

So mutated light chain status shows a longer TTFT than unmutated. Did I understand this correctly?

Patients with unmutated (UM) light chain genes displayed a 10-year treatment free probability of 32.4% versus 73.2% for those with mutated (M) genes (p < 0.0001).

[Mystic75]

Thank you so much, Neil, for taking the effort to post this. Really appreciated!

D.