Single-cell tracking of therapeutic cells using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry

Cellular therapy is emerging as a clinically viable strategy in the field of solid organ transplantation, where it is expected to reduce the dependency on conventional immunosuppression. This has produced a demand for highly sensitive methods to monitor the persistence and tissue distribution of administered cells in vivo. However, tracking cells presents significant challenges. In many cases transplanted cells are autologous with the immune system of the transplant recipient, and hence are invisible to typical methods of detection. To enable their differentiation, the cells must be labelled with a suitable, non-toxic and long lifetime label, prior to their administration to patients. In addition, administered cells represent only a small fraction of the recipient’s endogenous cells, which necessitates the use of an extremely sensitive detection method. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) is an exquisitely sensitive analytical technique, capable of imaging trace elements in complex samples, at high spatial resolution. [Continues.

A new freeware tool for image processing and its application to high speed LA-ICP-MS imaging

A new standalone, non-commercial software application has been developed to enable rapid generation of images from laser ablation – inductively coupled plasma – mass spectrometry data. The software locates peaks within raw data files and uses the peak locations to segment the data at appropriate intervals, enabling conversion of the data into a matrix of colour coded pixels. The app was developed in order to process baseline separated peaks produced by the latest generation of low-dispersion laser ablation systems, but it is equally applicable to rastered imaging using alternative laser ablation platforms. The peak recognition feature also has applicability to single cell and single particle ICP-MS applications. The app was demonstrated for the imaging of zinc in a stained section of rat retina tissue at lateral resolutions down to 1 µm. Less than two minutes was required for conversion of the raw data into a 60,000 pixel image

Development and use of “ICP-MS TuneSim”: a software app that allows students to simulate tuning an inductively coupled plasma mass spectrometer

A new app, freely available for Windows computers, has been developed to simulate tuning of an inductively coupled plasma mass spectrometer, on the basis of optimization data collected using a sector-field instrument. The app allows students to adjust parameters, including the torch position, gas flows, radio-frequency power, and guard-electrode state, while observing the signal for three “measured” variables in real time. The app has been used with a group of second-year undergraduate students to supplement theoretical material taught in an Atomic Spectrometry lecture course. The exercise familiarized students with key components of the instrument and demonstrated how multiple factors may need to be balanced when performing optimization

Acquisition of fast transient signals in ICP-MS with enhanced time resolution

In recent years, the field of ICP-MS has seen an increasing trend towards sampling systems and methods that produce short transient signals, rather than a continuous signal response. Fast data acquisition, readout and storage are crucial to take advantage of the wealth of information available from these approaches. However, many of the current generation mass spectrometers, in particular sector-field instruments, were not designed to cope with such short duration signals. This article reports the use of a commercially available multi-channel scaler board, which facilitates capture of TTL pulses from an ICP-MS detector at a user defined time resolution down to 100 ns. The board was used to profile 400–600 μs wide signals with 10 μs resolution, derived from the nebulisation of a 50 nm gold nanoparticle suspension. Furthermore, the benefit of a 100% duty cycle was demonstrated for ∼10 ms wide signals, following ablation of individual macrophage cells with a fast response LA-ICP-MS interface

Needles in haystacks: using fast-response LA chambers and ICP-TOF-MS to identify asbestos fibres in malignant mesothelioma models

Malignant mesothelioma is an aggressive cancer associated with exposure to asbestos. Diagnosis of mesothelioma and other related lung diseases remains elusive due to difficulties surrounding identification and quantification of asbestos fibres in lung tissue. This article presents a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method to identify asbestos fibres in cellular models of mesothelioma. Use of a high-speed laser ablation system enabled rapid imaging of the samples with a lateral resolution of 3 μm, whilst use of a prototype time-of-flight ICP-MS provided pseudo-simultaneous detection of the elements between mass 23 (Na) and mass 238 (U). Three forms of asbestos fibre (actinolite, amosite and crocidolite) were distinguished from a non-asbestos control (wollastonite) based on their elemental profile, which demonstrated that LA-ICP-MS could be a viable technique for identification of asbestos fibres in clinical research samples

Doubling sensitivity in multicollector ICPMS using high-efficiency, rapid response Laser Ablation Technology

The introduction of rapid response laser ablation cells and sample transport technologies to laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) has enabled signal pulse durations for a single laser ablation shot of less than 10 ms. These developments have resulted in marked improvements in analytical throughput, resolution, and sensitivity vital for the generation of large, highly spatially resolved elemental maps. The focus on mapping, particularly bioimaging, has obscured the possibility of applying the sensitivity advantage of rapid response technologies to other LA-ICPMS applications, such as high-precision isotope ratio analysis on multicollector (MC) ICPMS. In this work a commercially available rapid response sample transport system and a conventional configuration were compared for LA-MC-ICPMS analysis. Ablation of known reference materials demonstrated “sensitivity” or sample ion yield of 7–9% using the rapid response sample transport system, more than double that for the conventional setup. This increase in efficiency was demonstrated to improve precision for the Pb isotope ratio analysis of the MPI-DING reference glasses and improve the spatial resolution of Hf isotope ratio analysis of reference zircon

Single cell tracking of gadolinium labeled CD4(+) T cells by laser ablation inductively coupled plasma mass spectrometry

Cellular therapy is emerging as a promising alternative to conventional immunosuppression in the fields of haematopoietic stem cell (HSC) transplantation, autoimmune disease and solid organ transplantation. Determining the persistence of cell-based therapies in vivo is crucial to understanding their regulatory function and requires the combination of an extremely sensitive detection technique and a stable, long-lifetime cell labelling agent. This paper reports the first application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to perform single cell detection of T cell populations relevant to cellular immunotherapy. Purified human CD4+ T cells were labelled with commercially available Gd-based MRI contrast agents, Omniscan® and Dotarem®, which enabled passive loading of up to 108 Gd atoms per cell. In mixed preparations of labelled and unlabelled cells, LA-ICP-MS was capable of enumerating labelled cells at close to the predicted ratio. More importantly, LA-ICP-MS single cell analysis demonstrated that the cells retained sufficient label to remain detectable for up to 10 days post-labelling both in vitro and in vivo in an immunodeficient mouse model

Laser ablation inductively coupled plasma mass spectrometry as a novel clinical imaging tool to detect asbestos fibres in malignant mesothelioma.

RATIONALE: Malignant pleural mesothelioma is an extremely aggressive and incurable malignancy associated with prior exposure to asbestos fibres. Difficulties remain in relation to early diagnosis, notably due to impeded identification of asbestos in lung tissue. This study describes a novel laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) imaging approach to identify asbestos within mesothelioma models with clinical significance. METHODS: Human mesothelioma cells were exposed to different types of asbestos fibres and prepared on plastic slides for LA-ICP-MS analysis. No further sample preparation was required prior to analysis, which was performed using an NWR Image 266nm laser ablation system coupled to an Element XR sector-field ICP mass spectrometer, with a lateral resolution of 2 μm. Data was processed using LA-ICP-MS ImageTool v1.7 with the final graphic production made using DPlot Software. RESULTS: Four different mineral fibres were successfully identified within the mesothelioma samples based on some of the most abundant elements that make up these fibres (Si, Mg and Fe). Using LA-ICP-MS as an imaging tool provided information on the spatial distribution of the fibres at cellular level, which is essential in asbestos detection within tissue samples. Based on the metal counts generated by the different types of asbestos, different fibres can be identified based on shape, size, and elemental composition. Detection of Ca was attempted but requires further optimisation. CONCLUSION: Asbestos fibres detection in the lung tissues is very useful, if not necessary, to complete the pathological diagnosis of asbestos-related malignancies in medicolegal field. For the first time, this study demonstrates the successful application of LA-ICP-MS imaging to identify asbestos fibres and other mineral fibres within mesothelioma samples. Ultimately, high-resolution, fast-speed LA-ICP-MS analysis has the potential to be integrated into clinical workflow to aid earlier detection and stratification of mesothelioma patient samples