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Chapter 17

HLC immunoassays provide an additional tool for the management of patients with IIMM. The assays separately quantify the different light chain types of each immunoglobulin isotype (i.e. IgGκ, IgGλ, IgAκ, IgAλ, IgMκ and IgMλ, Chapter 9). The molecules are assessed in pairs to produce HLC ratios (e.g. IgGκ/IgGλ) in the same manner as κ/λ sFLC ratios. The HLC ratio provides information on both the involved (monoclonal) immunoglobulin (e.g. IgGκ in an IgGκ patient) and the uninvolved (polyclonal) HLC-pair (e.g. IgGλ in an IgGκ patient). When the concentration of the HLC-pair is below the normal reference interval, alongside an abnormal HLC ratio, this is termed “HLC-pair suppression”.

HLC assays are less labour-intensive and less subjective than serum electrophoretic techniques [36][376], and may overcome many of the known limitations of serum electrophoresis discussed above (including co-migration, dye saturation and broadly migrating monoclonal proteins, Section 17.4). For example, in Figure 17.6 two cases are presented in which monoclonal proteins co-migrate with other serum proteins bands, whereas HLC assays provide a quantitative result [912].

HLC assays were assessed in a large cohort of IIMM patients recruited to the IFM 2005-01 MM trial [36]. A total of 339 patients, comprising 245 with IgG (166 IgGκ, 79 IgGλ) and 94 with IgA (60 IgAκ, 34 IgAλ) isotypes were evaluated at presentation. The HLC data are summarised in Figure 17.7A and B, using Ig’κ/Ig’λ dot plots. The involved HLC concentration was greater than the upper limit of the normal range in the majority of patients (Tables 17.3 and 17.4), and all IIMM patients had the corresponding abnormal HLC ratio. Thirty-three percent (31/94) of the IgA patients could not be accurately quantified by SPE, due to co-migration with other serum proteins.

IgGκ MMIgGλ MM
Monoclonal Ig
by SPE (g/L)
Median
95% range
Total range
40.5
8.02 - 90
(4.9 - 109)
46.0
10.86 - 85.02
(5.7 - 86.0)
IgGκ HLC (g/L)
Median
95% range
Total range
33.0
5.60 - 91.81
(4.07 - 107)
0.41
0.12 - 5.84
(0.09 - 6.76)
IgGλ HLC (g/L)
Median
95% range
Total range
0.33
0.072 - 2.03
(0.04 - 3.19)
35.5
4.77 - 91.12
(4.58 - 97.3)
IgGκ/IgGλ HLC ratio
Median
95% range
Total range
93.52
5.13 - 864
(3.94 - 1334)
0.018
0.001 - 0.878
(0.001 - 1.05)

Table 17.3. Concentrations of IgG monoclonal proteins and IgG HLC in 245 patients with IgG MM [36].

IgAκ MMIgAλ MM
Monoclonal Ig
by SPE (g/L)
Median
95% range
Total range
34.0
11.35 - 88.55
(10.0 - 98.0)
28.0
3.46 - 62.1
(2.2 - 67.0)
IgAκ HLC (g/L)
Median
95% range
Total range
36.7
5.36 - 110.2
(3.49 - 125)
0.3
0.018 - 2.17
(0.018 - 2.65)
IgAλ HLC (g/L)
Median
95% range
Total range
0.072
0.017 - 1.13
(0.017 - 1.38)
30.1
1.95 - 49.9
(0.78 - 64.1)
IgAκ/IgAλ HLC ratio
Median
95% range
Total range
462
11.2 - 6020
(8.8 - 7352)
0.01
0.018 - 0.255
(0.001 - 0.32)

Table 17.4. Concentrations of IgA monoclonal proteins and IgA HLC in 94 patients with IgA MM [36].

Ludwig et al. [37] evaluated the HLC assays in 100 IgG and 56 IgA MM patients, all of whom had corresponding abnormal HLC ratios at diagnosis. Of note, accurate quantitation of the monoclonal immunoglobulin by SPE densitometry was not possible in 46% (26/56) of IgA patients and 4% (4/100) of IgG patients due to co-migration with other serum proteins. Similarly, in a study by Mirbahai et al. [377] comparing HLC data with SPE results at diagnosis of IgA MM all 210 patients had abnormal HLC ratios as determined by HLC assays (Figure 17.8A). However, accurate quantitation of the monoclonal protein was not possible in 40% (83/210) of patients by SPE; three of these are shown in Figure 17.8B.

Katzmann et al. [38] assessed the diagnostic sensitivity of HLC ratios in 365 IgG and 153 IgA MM patients at presentation. An abnormal HLC ratio was present in 97% of both IgG (354/365) and IgA (148/153) diagnostic samples. In IgA MM, the HLC ratio was more sensitive for detecting a monoclonal intact immunoglobulin than SPE (Section 4.2.5), and the authors recognised the utility of HLC assays in patients whose monoclonal protein migrates in the β-region.

In the IFM 2005-01 MM trial [36], the majority of IIMM patients had HLC-pair suppression (i.e. reduced concentrations of IgGκ in a patient with IgGλ IIMM). For IgGκ, IgGλ, IgAκ and IgAλ MM patients HLC-pair suppression was present in 99%, 92%, 93% and 69% of cases, respectively. Similar findings were reported by Ludwig et al. [903]. For one IFM IgAλ patient whose IgAλ HLC concentration was within the normal range (labelled 2 in Figure 17.7B), IgAκ HLC-pair suppression was present and the IgAκ/IgAλ ratio was abnormal. Interestingly, this patient and one additional patient (labelled 1 in Figure 17.7B) had highly elevated λ sFLC concentrations (8,500 mg/L and 103,000 mg/L, respectively). This was consistent with monoclonal λ sFLCs being the dominant monoclonal protein produced by the tumour. In such cases, sFLC analysis may be more informative for monitoring disease status (Chapter 18).

A number of studies have demonstrated that the degree of HLC-pair suppression varies greatly between patients (Tables 17.3 and 17.4) [36][903]. The IFM 2005-01 MM trial was the first to demonstrate that patients with higher concentrations of involved HLCs tended to have lower concentrations of uninvolved HLCs. This negative correlation between suppression and production was more significant in IgG patients (IgGκ: r = -0.456; p<0.0001; IgGλ: r = -0.310; p=0.005) than in IgA patients [904]. Similar findings were reported by Ludwig et al. [903].

Ludwig et al. [903] defined three categories of HLC-pair suppression: no suppression; moderate suppression (below the lower normal limit and up to 50% suppression), and severe suppression (a >50% reduction below the lower normal limit). Severe HLC-pair suppression was present in 54.5% (85/156) patients at diagnosis and tended to be more prevalent in IgG patients than IgA patients, but this did not reach statistical significance (57% vs 48.2%, p=0.0764). Severe HLC-pair suppression was associated with a significantly shorter survival and is described in more detail in Section 20.4.

Questions

  1. How often are sFLC ratios abnormal in IIMM?
  2. How frequently is quantitation of IgA monoclonal proteins not possible by SPE densitometry?
  3. How often are IgAκ/IgAλ HLC ratios abnormal in IgA MM patients at disease presentation?

Answers

  1. In approximately 95% of patients at clinical presentation (Section 17.2).
  2. Accurate quantitation by SPE is not possible in around 40% of IgA MM patients (Section 17.6).
  3. In 4 studies comprising 513 patients, IgAκ/IgAλ HLC ratios were abnormal in 99% of cases at clinical presentation (Section 17.6).
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References